The following article will coalesce several pieces of work from 2019 into one cogent story regarding a handful of communications mailed by the Zodiac Killer in 1970. For some, the following will be repetitive, for which I apologize. It will hopefully make the case that the Zodiac Killer was winding down his operations and ultimately revealing the answers to his Z340, Z32 and Z13 ciphers and codes, to which he knew were practically unsolvable without such a prompt. The Zodiac Killer was a narcissistic braggart, who boasted of his exploits and threatened all and sundry with the possibility of more murders and mayhem if his demands were not met, including the claim he had killed far more than could be accounted for. If we applied the same model to his ciphers and codes, we would have expected him to be unable to resist giving us the answers - or at the very least - some clues to break open his puzzles. The notion of a killer keeping deathly silent on the solutions to his codes for up to 50 years, runs contrary to everything we know about the Bay Area murderer during his brief but deadly reign. That is why I don't believe he did.

The story begins with the final thing he wrote on the July 26th 1970 Little List Letter, and finishes just two communications later with the October 27th 1970 Halloween Card. All the answers to his codes were contained in just three short months. The end of the Little List Letter read "PS. The Mt. Diablo Code concerns Radians and # inches along the radians". The Z32 was the easiest code to crack because the Zodiac Killer just gave us the answer above - the code concerned "Radians and inches along the radians". Why make it any more complicated than it has to be? A code of 29 unique symbols within a total of 32 characters is simply not solvable without a key - and there is insufficient wording on the 13 Hole Postcard, Halloween Card or Los Angeles Letter written in plain English to formulate any such key. The Z32 is even worse than giving us the English alphabet of 26 letters, replacing M with A, W with B and H with C and saying "now solve it". There is no transposition key present in the remaining three communications from October 5th 1970 to March 13th 1971, so if the Zodiac Killer was to be consistent in his inability to resist revealing his deeds, then the only realistic alternative is he gave us all the answers instead.

Not only did the Zodiac Killer give us the answer to the 32 character code on a separate line, he capitalized the first "Radians" to effectively tell us this was the beginning of the solution (he didn't capitalize the second "radians", so why the first). You need look no further than the Paul Stine police report to notice that the hashtag symbol is used in conjunction with a number. The Zodiac Killer by use of an arrow pointer underneath the hashtag, was telling us to replace the hashtag with a number value. The Mount Diablo map scale was 6.4 miles to the inch, so it is probably unsurprising that the "Mt Diablo code would concern inches". In this instance, I have placed the number 5 into place, giving us the answer to the code of "Radians and 5 inches along the radians" (which is 32 letters in length). The reason for 5 inches is self explanatory, because 4 or 6 inches from Mount Diablo to San Francisco would fall into the sea on the east and west side. The San Francisco element will be covered shortly. The Zodiac Killer also gave us a second set of crosshairs (shown below).

This was the first time the Zodiac Killer had ever placed an accentuated zero within his crosshairs alongside the acronym SFPD. This had to be the second clue to the location of the bomb. The hashtag and arrow signified the value of inches required, so this had to signify the radian value. By some massive stroke of luck (almost beyond belief), the bold, black accentuated circle fell over 246 degrees on a compass rose - which is 4 radians and magnetic north (17 degrees in 1970). Therefore, the target of his bomb must have been 4 radians and magnetic north, and 5 inches along the radians. 

All Zodiac's bomb threats were focused towards the San Francisco Chronicle and San Francisco Police Department, so placing this bomb location alongside the acronym SFPD should tell us that the threat was most likely focused toward a police station. By another massive stroke of luck, when we travel 4 radians and 5 inches from Mount Diablo, the target area for the bomb lies right by Ingleside Police Station. Allowing for a degree of flexibility of less than 1%, by the Zodiac Killer rounding off his radians and inches, along with the black circle diameter, no other San Francisco police station comes close. However, we need to find a location where a school bus would be traveling from north to south (with the sun to the east), that has an embankment on the right side (as displayed on the April 20th 1970 bomb diagram), with easy and covert access to that embankment, and within a few hundred feet from Ingleside Police Station. The Zodiac Killer certainly wouldn't have wanted to attract attention by parking on the road itself, but by accessing the incline from a secondary location - likely at the top of the embankment - he could achieve this task in relative anonymity. Fortunately for us, that location sits only 230 feet from Ingleside Police Station. The perfect location for the Zodiac Killer to target a school bus and thumb his nose at the San Francisco Police Department, with covert access to the top of the embankment via the car park of San Francisco City College.             

Then came the 13 Hole Postcard punched in the style of a 'Dick Tracy' code with a "red crucifix decoder". What are the chances that if we arranged the 13 holes into the shape of a cross and place it over the midsection of the 340 cipher both horizontally and vertically, it would reveal the wording "paradice" and "slaves"? Then, what are the chances that the Zodiac Killer would write "paradice" and "slaves" in his next communication in a cross formation on the card, accompanied by "sorry no cipher" in a cross formation on the inside of the Halloween Card envelope? - totaling three cross formations - but supposedly, all created for absolutely no reason whatsoever in just two communications. Isn't it more believable they were created for purpose. The Zodiac Killer could easily have written "sorry no cipher" just the once, but deliberately fashioned it this way to tell us that the 340 character cipher was not a cipher after all. It was simply a design of "paradice" and "slaves" as exhibited by the Halloween Card. Throw in a few bigrams, pivots and 'corrected sixth line', and hopefully it will look convincing. 

All these clues from the back end of the Little List Letter to the Halloween Card giving us the literal answer to both the Z340 and Z32 in "paradice" and "slaves", and "Radians and 5 inches along the radians". Could either the 13 Hole Postcard or Halloween Card give us the answer to the Z13 as well? Again, totally unsolvable because of its limited number of characters, the Zodiac Killer could either keep quiet for up to fifty years or give us the answer.

From a previous article: On January 29th 1970, the Yellow Cab Company put up a thousand dollar reward for any information leading to the arrest of the Zodiac Killer. In addition, the Teamsters Union which represents the Yellow Cab Company were reported in the San Francisco Chronicle to be considering offering a further reward on February 8th 1970 in the case of Paul Stine and Charles Jarman (another taxicab murder victim). The April 20th 1970 letter gave us the code and was immediately followed by "I am mildly cerous as to how much money you have on my head now". The October 5th 1970 postcard gave us the possible solution of "Fk, I'm crackproof" and was immediately followed by "What is the price tag now". These are the only two communications in which the Zodiac Killer asked the police the price of his capture. These two communications not only had a code and an answer that fitted the code, but both were followed by the exact same question. When the Zodiac Killer was designing his 13 Hole Postcard, it is very likely he had at his disposal a copy of his original April 20th 1970 letter, or the San Francisco Chronicle newspaper cutting below, to which he was now supplying the answer. This may have been the trigger that influenced him to repeat the phrase "how much money you have on my head now" into the very similar "What is the price tag now". The Zodiac Killer, in essence, had inadvertently bound both communications together through phraseology, as well as code and solution.   

The Zodiac Killer introduction would now give us his name (albeit his initials) in absence of his full name. It would also read fluently as a sentence, as follows: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof". Nobody realistically believed he was going to supply his full name, but this way he satisfies the promise in a restricted format. Two communications mailed nearly six months apart, with a solution that satisfies the code, as well as a satisfactory introduction to the code - and both followed by the same question.    

This isn't a case of dragging wording from the entire Zodiac collection of cards and letters, but using just the two crosshairs of the Little List Letter, followed by the 13 Hole Postcard and Halloween Card. The bold, black circle and "PS. The Mt. Diablo Code concerns Radians and # inches along the radians" to answer the Z32. The 13 holes, red cross, "paradice" and "slaves", and "sorry no cipher" to answer the Z340. And finally, "Fk, I'm crackproof" to give us a shorthanded version of his name, while still retaining his anonymity. The alternative is that the codes are genuine, the designs on the 13 Hole Postcard and Halloween Card are devoid of any purposeful meaning, and the big-headed, braggart called Zodiac, kept his lips 'butoned' for however many years afterwards.  

This has been covered before, but I just wanted to expand in a little more detail without pinpointing a particular location.

How embarassing is the notion of a 50-year-old unsolved cipher, that we were given the answer to in just thirty one days? - and an answer that came straight from the horse's mouth. The 32 Symbol Cipher solution was served to us on a silver platter in the July 26th 1970 Little List Letter using the Zodiac crosshairs and six words. 

When the Button Letter was mailed on June 26th 1970, the Zodiac Killer gave us a map of San Francisco and Vicinity with his crosshairs centered over Mount Diablo, stating "the map coupled with this code will tell you where the bomb is set." If we were to find a perceived bomb, it is fairly obvious we have to travel a certain angle and distance from the top of Mount Diablo to find the location. Therefore, the 32 symbol code, if it served any purpose whatsoever, had to contain a measurement in the form of degrees and distance. The map scale was 6.4 miles to the inch - so that will be the distance the Zodiac Killer has to employ from Mount Diablo to make any sense. The degrees he used was radians, because he told us so in the July 26th 1970 Little List Letter. The Zodiac stated "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". He is actually telling us that the 32 symbol code contains radians and inches in the solution.

"P.S. The Mt. Diablo code concerns (is about ) (has to do with) Radians + # inches along the radians". Any cipher expert such as David Oranchak, or quite frankly, any Joe Bloggs such as myself, will tell you that a 32 symbol code with only three repeating characters is unsolvable without a key. The Zodiac Killer was certainly no muppet - and clearly knew this when he concocted this jumble of random characters. But he gave us the key a mere 31 days later in the form of an arrow and a hashtag. He even gave us the answer of "Radians and # inches along the radians" on a separate line to distinguish the very fact. He then began the first "Radians" with a capital letter to emphasize this. We just had to key in the number. The symbol # is most commonly known as the number sign, The symbol is described as the "number" character in an 1853 treatise on bookkeeping, and its double meaning is described in a bookkeeping text from 1880. The instruction manual of the Blickensderfer model 5 typewriter (c. 1896) appears to refer to the symbol as the "number mark". Some early-20th-century U.S. sources refer to it as the "number sign", although this could also refer to the numero sign. A 1917 manual distinguishes between two uses of the sign: "number (written before a figure)"; and "pounds (written after a figure)". Mainstream use in the United States is as follows: when it prefixes a number, it is read as "number", as in "a #2 pencil" (indicating "a number-two pencil"). The one exception is with the # key on a phone, which is always referred to as the "pound key" or "pound". Thus instructions to dial an extension such as #77 are always read as "pound seven seven". Wikipedia.

All of Zodiac's bomb threats were mailed to the San Francisco Chronicle newspaper - even detailing the murder of San Francisco police officer Brian McDonnell on February 16th 1970, who suffered devastating and sadly fatal injuries when a bomb packed with fence staples exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood of San Francisco. The Zodiac constantly signed off his communications with the barbed acronym SFPD = 0 and threatened "there is more glory in killing a cop than a cid because a cop can shoot back". If that wasn't enough, the Phillips 66 Road Map was labelled San Francisco and Vicinity.  Based on a map scale of 6.4 inches to the mile, only 5 inches would land in San Francisco (4 and 6 inches would fall into the sea, other than Treasure Island). Fortunately, the Zodiac Killer gave us the angle from Mount Diablo, courtesy of his bold, black circle on the Little List crosshairs. It fell 4 radians (and magnetic north) clockwise from his arrowed pointer, around the clock face he provided. Radians are usually measured counter-clockwise, but the Zodiac Killer placed the bold circle exactly 4 radians "set to Mag.N" clockwise.

The answer was now extremely simple. All we had to do was insert a number in place of the hashtag, shown by the big flashing arrow pointing us in the right direction. The hashtag conveniently preceded "inches", so it's here we will slot in the number 5 - and bingo - we have our answer to the devilishly difficult 32 Symbol Cipher: "Radians + 5 inches along the radians" or "Radians and 5 inches along the radians".  By some quirk of fate, this phrase with the addition of the number 5, just happens to be exactly 32 characters in length. What an absolute criminal mastermind the Zodiac Killer was, creating a code that we only had to add one character to. As with all the best puzzles, the answer is usually hidden in plain sight. There is a possibility that the code reads "4 radians and 5 inches along the radian", but because the Zodiac Killer inserted one hashtag, it is more likely this is the only addition required.        

In the Little List communication it is apparent that Zodiac Killer gave us two prominent crosshairs: [1] with the accentuated black circle with SFPD=0 alongside, and [2] the extra large crosshairs with "P.S. The Mt. Diablo code concerns Radians + # inches along the radians" scrawled across it. Attaching these important additions was clearly done for purpose, thereby informing us of the radian value required, and the correlation between the crosshairs on the Phillips 66 Map and the measurements of radians and inches. The importance of a second set of crosshairs and their position, regarding the solution of the 340 cipher on November 8th 1969 could be significant in that case also.

With 29 unique characters in a 32 character code, any correlation between the characters and alphabetical solution is going to be minimal. What we do have in the solution above, is no word running from one line to the next, with the letter C beginning the word radians at the start and end of the code. As with any cipher, the Zodiac Killer had the opportunity to provide us with a key in later communications, which he effectively did for cipher 2, 3 and 4 when he gave us the answers literally word for word. What we have to consider are the three "cryptic messages" he gave us in three consecutive communications from July 26th 1970 to October 27th 1970. The Zodiac Killer was giving us the solutions to the ciphers before his campaign ended, albeit he wanted us to put in a modicum of effort. He told us on July 26th 1970 that the Mount Diablo code concerns "radians and 5 inches along the radians" verbatim. He then gave us the cryptic "Fk I'm crackproof" that fortunately slots nicely into the 13 Symbol Cipher in a cyclical nature. And finally, he gave us "paradice and slaves" in a cross formation (17X17) that mimicked the 340 cipher formation exactly (adding sorry no cipher in the identical formation on the Halloween envelope inner). How can three consecutive "cryptic messages" just happen to seamlessly fall into each cipher with no effort required?

We can place thousands of names into the 13 Symbol Cipher and then attempt to justify why this is correct by providing additional information on the subject. There have been hundreds of "solutions" to the 340 cipher, when we know only one can realistically be correct. This demonstrates the subjectivity of the 340 cipher to conform to what you had already decided upon before the decoding process began. You have the predetermined answer in your head and work towards that goal to the exclusion of all others. Our own biases will govern the answer we require. The 32 Symbol Cipher is too character variable to be decoded using standard cryptographic techniques, and therefore can literally give rise to an infinite number of possibilities, requiring only three characters to match. What better way to solve the ciphers than straight from the horse's mouth. The Zodiac Killer supplied us with 32 characters in the Little List Letter, 14 characters in the 13 Hole Postcard (that began and ended in the same letter), and 13 characters in the Halloween Card - all of which required no 'square pegs in round holes' technique to land unadulterated into every cipher. The notion of a braggart remaining tight-lipped about his ciphers, while still staggering around the streets of America some 50 years later, deserves a book all by itself.  

THE CODE SOLUTIONS BY ZODIAC

In the final instalment of this series we will attempt to refine the previous conclusions gleaned from the Zodiac Killer letters.
The Zodiac Killer stated on April 20th 1970 "I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station. Even though I talked about killing school children with one. It just wouldn't doo to move in on someone else's teritory.  But there is more glory in killing a cop than a cid because a cop can shoot back.  I have killed ten people to date. It would have been a lot more except that my bus bomb was a dud.  I was swamped out by the rain we had a while back." In the correspondence, the Zodiac Killer was referring to the murder of San Francisco police officer Brian McDonnell on February 16th 1970, who suffered devastating and sadly fatal injuries two months earlier, when a bomb packed with fence staples exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. The wording in the letter suggested that the Upper Haight neighborhood was not somewhere he was prepared to venture, but the suggestion of a school bus bomb and police station, when we take into account the SFPD positioned strategically by the bold, black circle on the Little List crosshairs and indicative of a location point, brings forth the notion of a school bus bomb under the noses of the San Francisco Police Department. Targeting a school bus within sight of a police station would certainly have dealt law enforcement a mighty blow.

The Zodiac Killer may have had a location in mind, despite the fact it was never followed through on - and this location has tentatively been identified as four radians (+magnetic north) and five inches along the radian in two previous articles. The exact position he had in mind to set up his photoelectric cells to detonate the bomb didn't necessarily have to conform to these measurements exactly, just be close enough to be rounded off by the Zodiac Killer. However, the other clues he gave us in the April 20th 1970 and July 26th 1970 communications were replete with information. We narrowed down a section on Google Maps between Daly City and Ingleside in San Francisco (between 246 and 249 degrees).

To narrow down the location even futher, we should be looking for a bus route approaching a school from north to south (so the sun is rising from the east on the left side). The roadway must have sufficient embankment on its right side to elevate photoelectic switch B. It must be within the parameters of 4 radians and 5 inches (allowing for a small margin of error). The addition of the pronounced black circle within the crosshairs of the Little List Letter in the form of SFPD=0, is suggestive of a location close to a San Francisco Police Department. In other words, the Zodiac Killer may have intended his "blast" right under the noses of law enforcement: "Hey pig doesnt it rile you up to have your noze rubed in your booboos?" Despite not knowing the exact topography of this location in 1970, I have found a site just 230 feet from Ingleside Police Station alongside Southern Freeway. 

The Zodiac Killer mailed us three parts of one cipher on July 31st 1969, to the San Francisco Chronicle, San Francisco Examiner and Vallejo Times-Herald. In his communication to the Chronicle he stated "In this cipher is my idenity". Bearing in mind this is the only portion of cipher with unsolved characters, it could be argued that any identity the Zodiac was offering would be found at the signing off phase in this cipher. It didn't really matter, because only four days later he gave us his identity in the form of "This is the Zodiac Speaking". The Zodiac Killer clearly made a mistake when taking his draught message into his 408 cipher, accidentally omitting the word "people" from the final offering. If we therefore conclude his original identity to be left was actually six characters shorter, it would have reduced the 18 unsolved characters to 12. Using the first-person singular pronoun of "I", his identity at the base of the 408 cipher would read "I am the Zodiac", to become "I am the Zodiac Killer" upon realization of his mistake. The Bay Area murderer literally gave us the exact wording to his unsolved 18 characters through his introductions in the Examiner and Herald letters (both communications began with "I am the killer"). Once we knew the pseudonym or identity as Zodiac on August 4th 1969, the conversion to "I am the Zodiac Killer" was the next logical step. This would become a habit for the Zodiac Killer, who would ultimately give us the exact wording to solve his remaining three ciphers. Not only would he give us the solutions to the codes, but his practice of using 'filler' with no apparent correlation to the solution would continue.  

The Zodiac Killer was no master criminal in the style of Moriarty, but he was nobody's fool either. To make the false assumption he didn't understand ciphers or codes when creating his remaining three offerings to the San Francisco Chronicle, would be a misguided one. Even somebody with limited knowledge of coding, knows that giving us a 32 character code with 29 unique characters within its framework, is practically unsolvable without a key. You can literally fill in the blanks as you choose. Therefore, the only realistic solution to the two smaller codes can come in two forms: [1] The Zodiac Killer can give us a key to decrypt the code, or [2] He can simply give us the answer. The Zodiac Killer may well have chosen option two, and given us the entire solution to all his three unsolved codes in subsequent communications. In fact, the possibilty exists that he supplied us with all the answers in three consecutive communications from July 26th 1970 to October 27th 1970 - in the Little List Letter (07/26/70), 13 Hole Postcard (10/05/70) and Halloween Card (10/27/70). The Zodiac Killer was likely giving us all the solutions before slipping back into anonymity. The newspaper article on November 16th 1970 by Paul Avery, linking Zodiac to the Riverside murder of Cheri Jo Bates on October 30th 1966, likely drew one final breath from the Zodiac Killer through 1971, before his race was run.    

The "key" phrases for the four codes are *in this cipher is my identity", "the Mt. Diablo code concerns radians and inches",  "Fk, I'm crackproof" and "sorry no cipher". The 408 cipher we have examined, so we will now tackle the 32 symbol code.

The Little List Letter mailed on July 26th 1970, one month after the Mount Diablo code (06/26/70), told us the code "concerns radians and # inches along the radians". It was as simple as adding in two figures to complete the code (hence the hashtag symbol denoting a number). The Zodiac gave us the exact wording for the solution, detailed here in a previous article. As stated above, the 32 symbol code with 29 unique characters couldn't be solved without a key or the answer. The Mount Diablo map and crosshairs were the framework, onto which we "coupled" the code for the location of the bomb. The answer was likely "4 radians and 5 inches along the radian", thereby giving us the solution word for word. An alternative to this solution (where only the hashtag is replaced by the number 5), is "P.S. The Mt. Diablo code concerns Radians and 5 inches along the radians". The Zodiac didn't necessarily have to incorporate the number 4 because we already knew the radian value from the bold, black circle provided on the Little List Letter crosshairs.

The next solutions were given to us in the 13 Hole Postcard - that may ultimately become the most important communication of them all. By combining the "red crucifix" decoder and 13 punch-holes in true "Dick Tracy" style, the Paradice and Slaves formation would be revealed, bisecting the 340 cipher along its mid-section both horizontally and vertically. See the article 'The Dick Tracy 340 Cipher'. The Zodiac Killer would again push us in the right direction by revealing the 340 was "sorry no cipher", by way of a cross formation on the Halloween Card envelope just 22 days later. If that wasn't enough, he wrote Paradice and Slaves in the identical formation it could be found within the 340 cipher. Three clues within the space of three weeks. See the article 'Zodiac Admitted 340 Not a Real Cipher'.

The Zodiac Killer also gave us the phrase "Fk, I'm crackproof" (upside down) on the 13 Hole Postcard. Apart from an expletive, the other viable option here, is the Zodiac Killer exclaiming that he is crackproof, preceded by his initials. The reason for this line of thinking, is the Zodiac Killer's wording before the 13 Symbol Cipher on April 20th 1970. The code is designed symmetrically and looks contrived, with three circled 8's fashioned at its center. The Zodiac Killer couldn't have supplied us with his name with any expectation it would be solved, because the code was simply too short and capable of providing us with thousands of solutions. However, he could provide us a solution to the code by giving us his initials. By doing it this way, he is in a roundabout way, giving us his name and a solution to the code that satisfies the introduction that preceded it: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is Fk, I'm crackproof".

This solution not only fits into the 13 Symbol Cipher, but reads continuously if imagined in circular fashion. The Zodiac Killer gave us three 8's within a circle (the symbol of infinity, and regeneration and rebirth within Christianity), with the letters K and M positioned ideally in the code to fit "Fk, I'm crackproof" around. There are three elements to this phrase: Fk, I'm, and crackproof. When the entire phrase is slotted around the letters K and M, the number 8 begins each element of the phrase (as shown below). As a side note, "Fk, I'm crackproof" can be spelled using the letters from the 32 Symbol Cipher characters, with only the F and K reversed.      

The Zodiac Killer had effectively given us the exact wording of "I am the Zodiac Killer", "Paradice and Slaves", "Fk I'm crackproof" and "radians and inches along the radian" - all of which can be inserted untouched into all four ciphers and provide us with solutions that don't require a key. The idea of a killer who constantly responded to the newspapers at every turn, somehow resisting the temptation to ever disclose the workings of his codes and ciphers is a difficult story to sell. If we are of the belief that the 32 and 13 character codes are simply too short and too variable to be solved, then without a key the Zodiac Killer likely supplied an alternative. In the case presented above, the "key" and "answer" could be described as exactly the same thing - and It was just a case of transferring the wording from one communication to another in at least three of the examples.

John Rose used Dave Oranchak's webtoy to create features of the Halloween Card in just an 81 character block around the center of the 340 cipher. Some have stated that the variability of the characters in this area of the cipher have allowed the freedom to manufacture such a result. While that may be the case, a larger pattern of Paradice and Slaves is replicated in a 17 X 17 formation along both same midsections, effectively mirroring the John Rose presentation. The fact that both are even achievable in the same cipher, is worthy of mention. The Bay Area braggart must have been itching to throw us a few clues to his unbroken codes and ciphers - so the notion that he didn't give us any before he disappeared into the twilight - is somehow difficult to swallow.   

In a previous article we concluded that the 32 character code mailed to the San Francisco Chronicle on June 26th 1970 stated "P.S. The Mt. Diablo code concerns 4 Radians and 5 inches along the radian", based upon the clues the Zodiac Killer gave us in the Little List Letter on July 26th 1970. This led to an area somewhere between Ingleside and Daly City on the south edge of San Francisco. The Zodiac drew us a bus bomb diagram on April 20th 1970, suggesting he was going to place two photoelectric switches on an embankment or hillside on the right side of the road. He stated it was to be set up early in the morning when the sun was rising in the east. The images below show the El Camino Real by Outer Mission, heading south, with the April 20th 1970 'Bus Bomb' diagram superimposed over it. The hillside to the right is the type required to place his two photoelectric switches - one by the roadside and the other higher on the banking. Any school bus heading along this road for early morning assembly, would have the sun rising in the east (shining left to right in the image below).

If the Zodiac Killer had any intentions of blowing up a school bus (which is unlikely), then he would be targeting the schoolchildren on their way to school in the morning. If the children were being bussed in from other parts of San Francisco for this particular school (St. Thomas More Catholic School), then traveling from the north and east, the bus driver could be using Highway 101 and Interstate 280 in the direction shown by the red line below (recommended on Google maps). The blue circle is 4 radians (+ magnetic north), and 5 inches from Mount Diablo, satisfying the 32 character cipher and Zodiac's statement of "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". The highway under the blue circle is traveling south with the sun to the east in the morning - and is heading toward St. Thomas More Catholic School (just 1.37 miles away).      

The Zodiac Killer stated on April 20th 1970 "I am mildly cerous as to how much money you have on my head now.  I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station.  Even though I talked about killing school children with one. It just wouldn't doo to move in on someone else's teritory.  But there is more glory in killing a cop than a cid because a cop can shoot back.  I have killed ten people to date. It would have been a lot more except that my bus bomb was a dud.  I was swamped out by the rain we had a while back. The new bomb is set up like this. Sun light in early morning. A + B are photoelectric swiches when sun beam is broken A closes circut. B opens circut, which makes B the cloudy day disconect so the bomb won't go off by accid. PS I hope you have fun trying to figgure out who I killed".

​​The choice of words the Zodiac used at the beginning of this communication were unfortunate, had his target been children from St. Thomas More Catholic School. The school was named after Thomas More, an English lawyer, social philosopher, author, statesman, and noted Renaissance humanist. He was also a Chancellor to Henry VIII, and Lord High Chancellor of England from October 1529 to 16 May 1532. He was sentenced under the Treasons Act 1534 and decapitated with an axe. Therefore, it was very unfortunate that the Zodiac Killer should state "I am mildly cerous as to how much money you have on my head now".

There are several other schools in this area between Ingleside and Daly City, but we must remember that it is the bus he was targeting, not the school. Therefore, we should prioritize the roadways in this area (shown by the red rectangle), from the perspective of a bus traveling south, with its left side facing east.

The Zodiac Killer mailed a bomb threat on June 26th 1970, stating "the map coupled with this code will tell you where the bomb is set." One month later, realizing the inadequate information he had provided, the Zodiac Killer mailed another communication stating "P.S. The Mt. Diablo code concerns Radians + # inches along the radians", while adding some crosshairs with a black circle and the addition of SFPD = 0 alongside it. The overwhelming majority of the Zodiac Killer's communications were mailed to the San Francisco Chronicle and his taunting of the police heavily focused on the San Francisco Police Department from 1969 to 1971. If a bomb was to be set, then the Zodiac Killer was likely targeting San Francisco. He almost certainly never followed through on any of these threats, but it would be interesting to discover where his intended focus was, and find the solution to the 32 character code supplied on June 26th 1970. This topic has been covered before, but this will iron out a few problems experienced with previous articles.

The Zodiac Killer couldn't resist responding to the newspapers when he was asked to supply more details about his crimes, as demonstrated when he delivered the August 4th 1969 'Debut of Zodiac' Letter. He responded in a seven-page letter to refute the claims of Captain Martin Lee of the San Francisco Police Department, when his October 13th 1969 letter was disbelieved. He also wasn't averse to claiming various murders, disappearances and abductions that had featured in the newspapers. Despite this, the overwhelming consensus exists of a killer who remained resolutely silent on the workings of his three unsolved cryptograms or codes. However, there is every chance he gave us the exact wording that permeated the 340 cipher, to which he fashioned into the Halloween Card one year later. This was explored in the article Zodiac Admitted 340 Not a Real Cipher. I also believe he gave us the exact wording in the July 26th 1970 'Little List' Letter to solve the 32 character cipher a month earlier.

A radian value is approximately 57.3 degrees, which travel counter-clockwise. However, the Zodiac Killer placed a form of numerical clock face around the circumference of his crosshairs on the Mount Diablo map and stated that it be set to Magnetic North (about 17 degrees in 1970) - so it was considered that he had formulated his radians to run clockwise. The only radian value that can fall near San Francisco when a line is subtended from Mount Diablo, is 4 radians + 17 degrees = 246.2 degrees. Three and five radians doesn't fall anywhere near San Francisco. Therefore, a bomb set in San Francisco would have to be around the 4 radian + Magnetic North value. The bold, black circle present on the 'Little List' Letter crosshairs, falls in the region of 246.2 degrees - bearing in mind it is just a rudimentary sketch. Shown on the map above, is 2 radians counter-clockwise from True North (which would land at 245.4 degrees clockwise from True North). Both examples landing in the same region of the map. Daly City Police Department sits around 246 degrees from Mount Diablo, but resides in San Mateo County (shown by the red line). Ingleside Police Station (shown by the green line) sits closer to 249/250 degrees, but resides in San Francisco. If the Zodiac Killer had chosen a target in this region, we might expect the radian value to be only a rough guide. But it is clear, that if he is referring to a radian value, then it has to be a whole number - and it can only be 4 radians. 

Likewise, the value of inches can only be 5, if we are referring to a bomb threat in San Francisco. The scale on the Mount Diablo map is 6.4 miles to the inch. Four and six inches (25.60 and 38.40 miles) both fall into the sea on the east and west coast of San Francisco. So, unless the Zodiac Killer was wearing scuba gear and was planning to blow up an underwater school bus, the value of inches had to be the whole number of 5. When 5 inches is subtended from Mount Diablo, it gives us a value of 32 miles (somewhere in the red box below, allowing for a small margin of error). This margin of error has also been applied vertically to encompass Ingleside Police Station, bearing in mind that SFPD = 0 threat. Whether the mention of SFPD in the crosshairs on the 'Little List' Letter implies a specific threat to San Francisco itself, or somewhere close to San Francisco is unknown - but the region of San Francisco seemed the primary focus of the Zodiac Killer's communicaions during this two-year period. 

Now that we know a threat in the San Francisco region has to be subtended using the whole numbers of 4 radians and 5 inches, let us use the Zodiac's own words to complete the 32 character cipher, just like the words Paradice and Slaves from the Halloween Card was used to fill in the 340 cipher. The Zodiac Killer wrote on July 26th 1970: "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". But notice the hashtag.

The symbol # is most commonly known as the number sign, The symbol is described as the "number" character in an 1853 treatise on bookkeeping, and its double meaning is described in a bookkeeping text from 1880. The instruction manual of the Blickensderfer model 5 typewriter (c. 1896) appears to refer to the symbol as the "number mark". Some early-20th-century U.S. sources refer to it as the "number sign", although this could also refer to the numero sign. A 1917 manual distinguishes between two uses of the sign: "number (written before a figure)"; and "pounds (written after a figure)". Mainstream use in the United States is as follows: when it prefixes a number, it is read as "number", as in "a #2 pencil" (indicating "a number-two pencil"). The one exception is with the # key on a phone, which is always referred to as the "pound key" or "pound". Thus instructions to dial an extension such as #77 are always read as "pound seven seven". Wikipedia.

The Zodiac Killer could easily have left the phrase as "P.S. The Mt. Diablo code concerns Radians + inches along the radians", but deliberately forced the hashtag into place to denote a number - that number being 5. The phrase would now read "P.S. The Mt. Diablo code concerns Radians + 5 inches along the radians". We know that any threat on San Francisco had to fall in the 4 radians value, so we can complete the phrase: "P.S. The Mt. Diablo code concerns 4 Radians + 5 inches along the radians". But because we have now added a specific "5 inches" to be subtended along the line of the 4th radian, the correct phrase would read "P.S. The Mt. Diablo code concerns 4 Radians + 5 inches along the radian".
An alternative to this solution (where only the hashtag is replaced by the number 5), is "P.S. The Mt. Diablo code concerns Radians + 5 inches along the radians". The Zodiac didn't necessarily have to incorporate the number 4 because we already knew the radian value from the bold, black circle provided on the Little List Letter crosshairs.

There is no way this code could realistically be solved with 29 unique characters and no key. But fortunately the Zodiac Killer realized this and gave us the answer one month later. He did the same with Paradice and Slaves in the Halloween Card, to help our understanding of the 340 cipher. So, where is the answer to the '13 Symbol' cipher mailed on April 20th 1970?

THE LOCATION OF THE BOMB [PART TWO]

Question marks have always hung over the October 5th 1970 '13 Hole' or 'Pace' Postcard as to whether the author was the Zodiac Killer or a copycat. This article will hopefully go a long way to convince people that the communication was indeed mailed by the Bay Area murderer. The Zodiac Killer wrote the lengthy 'Little List' Letter on July 26th 1970, beginning the correspondence with his intentions for his slaves in paradise, followed by the torture methods he was going to apply, before finishing with the plagiarism of Gilbert & Sullivan's The Mikado, from the Act As Some Day it May Happen. The crucial thing to remember here, is that this communication was withheld from the newspapers and public alike, so by October 5th 1970 when this postcard was postmarked, the author (if not Zodiac} was totally unaware to the contents of the Little List Letter. The Zodiac Killer could have been reemphasizing his victim total of thirteen, or a copycat could have been suggesting thirteen victims for the first time, unaware that the Little List Letter had ever been mailed. Therefore, this is no help in determining whether the author of the '13 Hole' Postcard was the Zodiac Killer or not. We need to look at the wording on both communications back to back.

The first thing to notice on the '13 Hole' Postcard is the crucifix and number 13 in close alliance - extremely relevant when we consider the Zodiac Killer using the phrase "I shall (on top of everything else) torture all 13 of my slaves that I have waiting for me in Paradice" in the Little List Letter. The crucifix, a symbol of Christianity and the progression from life on earth to the paradise of heaven, is further cemented by the October 27th 1970 Halloween Card where the Zodiac Killer actually combines all three elements. However, if you are also a skeptic of the Halloween Card, then we need to focus entirely on finding a link between the '13 Hole' Postcard and the previously unpublished Little List Letter, both eventually released in tandem with one another on October 12th 1970 in a newspaper article by Paul Avery. Below I have separated the Little List Letter into its constituent parts - his promise of torture, his methods of torture and the search for victims.            

The Zodiac Killer refers to his victims in the plural and in the future tense, beginning his torture methods with "Some I shall tie over ant hills and watch them scream + twich and sqwirm. Others shall have pine splinters driven under their nails + then burned. Others shall be placed in cages + fed salt beef untill they are gorged then I shall listen to their pleass for water and I shall laugh at them". He uses the word "some" to begin his rhetoric, then continues with his Little List of potential victims, sourced from As Some Day it May Happen, beginning with "As some day it may hapen that a victom must be found". Therefore, is it any great surprise that the Zodiac Killer having noted his lengthy communication was not published in the newspapers, would begin the '13 Hole' Postcard in the past tense, stating "The pace isn't any slower. In fact it's just one big thirteenth. 'Some of them fought it was horrible'".

The Zodiac Killer is effectively saying that he had now tortured his victims in paradice and "some of them had fought". He is telling Paul Avery and the San Francisco Chronicle newspaper he had made good on his promises. This strongly suggests that the author of the '13 Hole' Postcard knew the contents of the July 26th 1970 Little List Letter, thereby cementing the notion that the Zodiac Killer was the author of both communications. The alternative, is that a copycat just threw together a random postcard that not only continued the theme of the previous letter accidentally, but was adopted by the Zodiac Killer in the October 27th 1970 Halloween Card and the following March 13th 1971 letter, where the Zodiac Killer stated "This is the Zodiac speaking Like I have allways said, I am crack proof". The copycat scenario proliferated by many, a sensational subplot to discredit certain Zodiac communications and attacks, where no merit for such claims exist. 

The other notable element of the '13 Hole' Postcard is the Mon, Oct 5, 1970 attribution in the top right corner. The Zodiac Killer did recite the Gilbert & Sullivan Act As Some Day it May Happen. So was Monday, October 5th the day something happened - and the reason he added a specific date for the very first time?   

It has been claimed by Kathleen Johns that she received phone calls and a Halloween card (likely October 1970) from the Zodiac Killer, addressed "To the woman in the blue station wagon". This greeting card may have been simultaneously mailed with the Halloween card to Paul Avery on October 27th 1970, so it would be interesting to search for correlations between the 10/27/70 Halloween card and the abduction of Kathleen Johns. If the two Halloween cards were mailed by the Zodiac Killer around the same timeframe, then the inclusion of "by fire" alongside "To the woman in the blue station wagon" would leave little doubt that the two are connected. Traveling clockwise around the 10/27/70 Halloween card, the Zodiac Killer presented the weapons he used in the correct order of their appearance up to March 23rd 1970 - By Gun, By Rope, By Knife and By Fire. The young woman apparently forwarded this card she received to newspaper reporter Paul Avery, but like everything else in the Zodiac case it disappeared into the ether (assuming her story is true). It has been claimed that if the Zodiac was responsible for the mailing of a Halloween card to Kathleen Johns, then he was responsible for her abduction, because no mention of her driving a blue station wagon was published in the newspapers. Without trawling the entire newspaper collection from 1970, I cannot verify this detail one way or another. 

As has already been suggested, the Zodiac Killer (or her abductor) would have had ample time to rummage through her vehicle after her ordeal was over and search for any letters or documents that contained her address and telephone details. Having deposited his fingerprints all over her vehicle, this may explain why he thought it easier to torch her 1957 Chevrolet, and why he returned to her vehicle after the 2-hour abduction - to gather information for his future correspondence. 

Kathleen Johns effectively contradicted herself when she named Lawrence Kane as her likely abductor that night, because he would have been 45 years of age on March 22nd 1970. She described her abductor as white, around 30 years of age, 5'9" in height, 160 lbs, dark hair, clean-cut and having the traits of a serviceman. So how can we reconcile this difference?

For people who still believe that the Zodiac Killer was 20-30 years of age during his attacks, while also believing that the Kathleen Johns abduction was the work of the Zodiac Killer, we have to consider the amount of time she spent in his vehicle and her detailed description regarding the interior of the vehicle. Kathleen described his car as messy and had noticed men's and children's clothing scattered about, along with books and papers, a black rubber-handled flashlight, and two colored plastic scouring pads on the console dashboard. Kathleen estimated that the smaller patterned T-shirts were designed in the age range of 8-12 years. Unless the Zodiac Killer was a traveling salesman selling children's clothing, or had borrowed the vehicle, a reasonable assumption would be that these haphazardly scattered clothes were part of a family vehicle. If Kathleen Johns upper estimate of the clothing was correct at 12 years - and a 20 to 30 year Zodiac conceived this child - he would have been approximately 8 to 18 years of age at the time (12 to 22 at the lower estimate), making the case for a Zodiac Killer of at least 30 or above more believable. If you don't accept that these clothes were necessarily the clothing of the Zodiac Killer's chidren, then an alternative explanation is necessary.

In 1972, the average age of fathers of newborns in the U.S. was 27 - so if the Zodiac was the biological father of the 12-year-old who wore the clothing present in his vehicle, then the statistical average would suggest a killer of about 39 years of age in 1970, in closer proximity to the age of Lawrence Kane (who she identified as her abductor), and very close to the average age of 40 described by three sets of eyewitnesses at Presidio Heights.   

Howard Davis wrote on the old zodiackiller.com message board that "This woman felt that the PD rednecks were put off by Kathleen Johns hippy appearance and really didn't put much credence or interest in her recounting the event of that night". Was the same conclusion on the appearance of Kathleen Johns drawn by the Zodiac Killer, who paraphrased the Gilbert & Sullivan's Mikado in his communication on July 26th 1970, opening with the lines from 'As Some Day it May Happen', performed by Ko-Ko. The beginning of Act One stated "As some day it may hapen that a victom must be found. I've got a little list. I've got a little list, of society offenders who might well be underground, who would never be missed, who would never be missed".

Did the Zodiac Killer regard Kathleen Johns hippy tendencies as part of the counterculture or underground movement that he had on his "little list".- people that wouldn't be missed? The letter mailed only two days earlier to the San Francisco Chronicle would suggest so. He wrote on July 24th 1970, threatening "This is the Zodiac speaking. I am rather unhappy because you people will not wear some nice (Zodiac symbol inserted)  buttons. So now I have a little list, starting with that woeman + her baby that I gave a rather intersting ride for a coupple howers one evening a few months back that ended in my burning her car where I found them". The phrase "I now have a little list, starting with that woeman + her baby" appeared to suggest that her escape would be short-lived and that some day it might happen. It appeared that three months later she may still have been in his sights, when she apparently received a Halloween card from her abductor at her home address. He had promised to "start" with her and he wasn't finished yet.

The 'As Some Day it May Happen' verse ended with "But it really doesn't matter whom you place upon the list, for none of them be missed, none of them be missed". Sadly, Kathleen Johns is no longer with us and deeply missed by her loved ones - but fortunately for her family and friends, it wasn't at the hand of the Zodiac Killer.

Alan Keel, Criminalist at the San Francisco Police Department, San Francisco, California from 1996 to 1999 "revealed that there were two letters in possession of the department that, in contrast to the "true" Zodiac letters, had abundant saliva and DNA-containing oral epithelial cells on them, that DNA was easily extracted from these two letters, and that the DNA extracted from these two letters matched between them. These two letters were considered forgeries, since the "true" Zodiac verifiable letters had not been licked by the sender". Mike Rodelli, an avid Zodiac researcher, who conversed with Alan Keel, revealed "In contrast (to earlier communications), Keel analyzes two other letters, one of which is the 1978 forgery, and finds that this letter and one of the 1974 letters are loaded with saliva and cells. He then easily extracts DNA from both of these letters using the more primitive DNA technology of that time and finds that the DNA matches between those two letters, thus proving that one person sent both".  Mike Rodelli.

​If you take a look at the San Francisco Police Department DNA report, the 1974 Exorcist letter is the only letter that year to produce any viable results, described as "cells found". The S.L.A letter was totally disregarded, and the "Citizen" and "Red Phantom" communications had no entry in comments. If Alan Keel is correct in his assertion, then the Exorcist letter would enter the classification of unlikely Zodiac correspondences - ones that had "been licked by the sender". 

In the latest round of DNA testing in the Zodiac case, two of the three July 31st 1969 communications have again come under scrutiny. These were unavailable at the time the San Francisco Police Department DNA testing was undertaken. It is apparent that these letters have struggled to give up their secrets, as have other communications listed in the report, which includes the October 13th 1969 'Paul Stine' letter, the November 8th 1969  'Dripping Pen' card, the November 9th 1969 'Bus Bomb' letter, the December 20th 1969 'Melvin Belli' letter, the April 20th 1970 'My Name Is' letter, the April 28th 1970 'Dragon' card and the June 26th 1970 'Button' letter. In total, nine consecutive communications that, it is fair to say, have produced little in the way of a recognizable DNA fingerprint. Most of these are labelled in comments as "few cells".

The only remaining communications in the DNA report subsequent to June 26th 1970 which produced any notable results, classified as "cells found", were:
[1] The July 24th 1970 'Kathleen Johns' letter.
[2] The July 26th 1970 'Little List' letter, and
[3] The January 29th 1974 'Exorcist' letter.
And all three had one crucial element in common - The Mikado. 

The 'Kathleen Johns' letter began the trilogy by stating "So now I have a little list, starting with that woeman + her baby that I gave a rather intersting ride for a coupple howers one evening a few months back that ended in my burning her car where I found them".  This would be continued two days later with the paraphrasing of two of Gilbert and Sullivan's acts from The Mikado. The first section of the 'Little List' letter pulls lines from the A more humane Mikado, where the author uses the words billiard along with crooked cues and twisted shoes.
This correspondence goes on to paraphrase Gilbert and Sullivan's  As some day it may happen, performed by Ko-Ko, as did the future correspondence of the Exorcist Letter in 1974, when reciting Tit-Willow from Ko-Ko's On a tree by a river, part of Act Two.  

We don't know the exact concentrations of DNA retrieved from these three communications, but it is evident that these were the only three letters classified as "cells found" - and all three made reference to The Mikado. If "cells found" could be proven as "saliva" found, and the "true Zodiac verifiable letters had not been licked by the sender" according to Alan Keel, then this could indicate that all The Mikado letters were not authored by the Zodiac Killer. An extremely hard notion to accept when we look at the handwriting and design of each of these correspondences. 

One can understand why certain sections of the Zodiac communications were withheld from the public, such as his bomb diagrams - yet the entire July 26th 1970 'Little List' letter was not released to the newspapers until October 12th 1970. This innocuous correspondence for the most part was withheld for two and a half months until it featured in a San Francisco Chronicle article entitled 'Gilbert and Sullivan Clue to Zodiac', in tandem with the subsequent October 5th 1970 '13 Hole' postcard. If the 'Little List' letter and '13 Hole' postcard were authored by the Zodiac Killer, then it is notable that, despite putting a lot of effort into this rather lengthy correspondence on July 26th 1970, he failed to make any issue about the complete absence of newspaper coverage that this letter received when he mailed his next correspondence. It is believed he repeated his victim count of 13 because his last letter hadn't been published in the newspapers. But could it have been the case that the Zodiac Killer wasn't reaffirming the victim count of 13 because his previous correspondence wasn't published, rather, he was unaware somebody had mailed the 'Little List' letter in his name? Hence his lack of concern about "front page coverage", or for that matter, any coverage at all. 

If the Zodiac Killer hadn't written any of The Mikado communications, then he also wasn't claiming the abduction of Kathleen Johns on March 22nd 1970. In fact, the notion of a killer driven by the theatrical librettos of Sir William Schwenck Gilbert would be quashed entirely. It is extremely difficult to sell a story of a Zodiac Killer who didn't author any of The Mikado communications, let alone all of the 1974 communications - so the curtain call will be cancelled for this performance only. 

The Zodiac Killer mailed the 'Button' letter and Phillips 66 Map on June 26th 1970 overlaying his crosshairs over Mount Diablo. Just a month later, realizing the clues in the Button letter were insufficient, he gave us the answer in the 'Little List' letter declaring "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". The crosshairs with the bold SFPD = 0 were telling us exactly where he planned to 'set his bomb'. By identifying the location in degrees, using a black, bold circle and coupling it with a 'dig' at the San Francisco Police Department, he was effectively giving us the target and the location. His target was the San Francisco Police Department subtended at an angle of 246 degrees from true north. Bearing in mind his bomb threats were focused in San Francisco, all we had to do was find the police department. How experienced the Zodiac Killer was regarding radians is unknown, but he designed a form of clock face with a directional marker pointing true north and then stated "0 is to be set to Mag.N" (which was approximately 17 degrees in 1970). We don't actually need to know how many radians he intended, from which point, and whether they were meant to travel clockwise or anticlockwise around the clock face, because the bold, dark circle is already the answer.   

On the left I have combined the crosshairs from the 'Button' and 'Little List' letters. The bold, dark circle is 246 degrees around the circumference (which is 4 radians + magnetic north). A radian is 57.3 degrees, so 4 X 57.3 + 17 degrees = 246 degrees. If we deduct 2 radians from true north we get 360 - 114.6 = 245.4 degrees. So, whether we use 2 radians anticlockwise from true north or 4 radians clockwise from magnetic north, the result falls within the circumference of his bold, dark circle (246 and 245.4 degrees). 

Drawing a line through this bold, dark circle from Mount Diablo and across San Francisco, it passes near only one police station, that of Ingleside. It isn't absolutely accurate, but it is the closest police station the measurement relates to. This is why he added SFPD next to the bold, dark circle rather than placing it at the foot of his letter in customary fashion. His bomb was to be set in the vicinity of the San Francisco Police Department at Ingleside. Whether he actually meant it is debatable, but it was the threat that was likely his main goal - sowing more fear into the heart of San Francisco.

The Zodiac Killer made many bomb threats in the 1970s, including references to "black power" in the April 28th 1970 'Dragon' card, along with his Symbionese Liberation Army letter in 1974. This has led some to ponder if the Zodiac Killer was somehow affiliated to a radical group, or possibly infuriated by groups such as the Black Liberation Army or Black Panthers, stealing the limelight away from his dwindling publicity: "I would like to see some nice Zodiac buttons wandering about town. Everyone else has these buttons like, black power, melvin eats bluber, etc". The Zodiac Killer may have been mailing correspondence well into 1971, with communications such as the July 13th 1971 'Monticello' card, 148 character cipher, and quite possibly, the unseen DMV letter. At this period of time, it appeared as though the Zodiac Killer was desperately attempting to connect himself to the murders of Debra Gaye Furlong, Kathy Ann Snoozy and Kathy Bilek, all savagely stabbed in excess of fifty times.   

Mary Alice Willey arrived in San Francisco in 1969, making some questionable alliances, including the black power movement. "She became a strident devotee of George Jackson, the charismatic but militant San Quentin inmate who had gained international fame for his best-selling prison classic, "Soledad Brother." She wrote letters to Black Panther Johnny Spain, who was also incarcerated at San Quentin. And she began associating with members of the Black Liberation Army, a violent offshoot of the Black Panthers that would become implicated in the Aug. 29, 1971, killing of a police officer at San Francisco's Ingleside Station. There is reason to believe that Mary Alice may have played a role in the attack and the slaying of Sgt. John V. Young". Read more at the San Francisco Chronicle. 

While in San Francisco she dated a fellow student, Patrick Warren McDowell, who claimed he belonged to the Symbionese Liberation Army, a group ultimately responsible for the kidnapping of Patty Hearst in 1974. In February 1971 he was arrested for the failed robbery of the Sugar Bowl Ski Lodge near Lake Tahoe, having borrowed Mary Alice Willey's car.

If the Zodiac Killer was still closely following the news in 1971, as it appears he was, regarding Snoozy, Furlong and Bilek, then it wouldn't have gone unnoticed that the Ingleside Police Station he had threatened to bomb just over a year ago, had now come under attack. On August 21st 1971 a gun was smuggled to George Jackson in San Quentin Prison. As Jackson was being escorted back to his jail cell, a guard noticed the gun. Jackson raised the weapon and, paraphrasing Vietnamese revolutionary leader Ho Chi Minh, declared: "This is it, gentlemen. The dragon has come." As he later ran across the prison courtyard, a guard opened fire killing Jackson instantly. 

On August 29th 1971, a woman who bore a resemblance to Mary Ann Willey, wearing a blond wig, entered Ingleside Police Station to report a stolen purse. "Police have long thought the woman who had come to the station to report her stolen purse was a lookout connected to the Black Liberation Army, and they believed that woman was Mary Alice". Chronicle.  A short time later several black men entered the station and murdered John V. Young with a shotgun through the grill of the reception desk. Within two weeks of this attack Mary Alice Willey had vanished. 

On September 11th 1971 a worker stumbled across the body of a woman while driving along the Delta-Mendota Canal in Stanislaus County near Patterson - close to the abduction site of Kathleen Johns on March 22nd 1970. There was no evidence of sexual assault, but she had been stabbed at least 65 times, and her murderer had attempted to sever her fingers and hands. An identification was not made. 

"In March 1970, a pregnant woman and her 10-month-old daughter were abducted near Modesto by a man who drove them around the valley and, according to some police reports, threatened to kill them. Kathleen Johns and her daughter ultimately escaped and hitched a ride to the police station in Patterson. While giving her statement, Johns reportedly saw a drawing of the Zodiac Killer and claimed he was the one who abducted them.

Johns' conflicting statements, though, cast doubt upon whether she had, indeed, encountered and survived the Zodiac. The murder Hedrick is revisiting happened just 18 months after that abduction. The Zodiac claimed 37 kills, though only the five were confirmed. There's nothing to suggest the Zodiac Killer, who never was captured, claimed credit for this murder, sheriff's Detective Marc Nuno said". Read more at The Modesto Bee.

Nearly four decades later, in September 2008, her body was exhumed from Patterson cemetery, and using a forensic sculptor to reconstruct her face and modern DNA testing, she was finally identified as Mary Alice Willey.​

The Zodiac Killer gave us a map code on June 26th 1970, stating the "map coupled with this code will tell you where the bomb is set." To this day no bomb has been unearthed and the threat was likely an idle one, designed primarily to create fear within the American community. However, the map and code were real, and the answer to both has probably been sitting in plain sight for nearly fifty years. The Zodiac, aware that the '32 Symbol' cipher was unable to be broken because it had 29 different characters, gave us all the answers one month later when he mailed the July 26th 1970 'Little List' letter.
The numerous suggested bomb threats were all mailed to the San Francisco Chronicle, so it was evident that his threats were focused on San Francisco itself - which is why the Mount Diablo map included San Francisco and Vicinity rather than just the area around Mount Diablo. The 'Little List' letter was replete with all the information required to crack his map code.
In the 'Button Map and Code' letter the author gave us the "map coupled with this code will tell you where the bomb is set," and just one month later, clearly told us that the code "concerns Radians & # inches along the radians" Therefore, the code will at least contain the words "radians" and "inches" in the answer - and that may very well be the case. In fact, it tells us exactly where the intended bomb was to be set, within the design of the crosshairs with the bold black circle. With the threats geared towards schoolchildren and police it is apparent that these are the likely targets. The reference to SFPD = 0 being incorporated within the crosshairs, along with an accentuated black, bold zero suggesting a location, should be the biggest clue of all. His intended target was the San Francisco Police Department - the location of which can be found within this bold circle. 
The Zodiac Killer referenced "radians" and "inches" (not parts of radians and inches), so with probably just the use of a ruler back in 1970 the Zodiac Killer would measure his intended target this way. Therefore, if he is one eighth of an inch off in his measurements we can forgive him this textual indiscretion. Fortunately, we have Google maps, so the task is much easier.
With an intended target in San Francisco, there is only one answer possible to the "radians" and "inches" conundrum, and it's governed by geography. 1 radian = 57.3 degrees, 2 radians = 114.6 degrees, 3 radians = 171.9 degrees, 4 radians = 229.2 degrees and 5 radians = 286.5 degrees. This is detailed crudely on the map below.
It is apparent that Zodiac wasn't referring to 5 radians, as a line subtended from Mount Diablo at this angle would pass north of San Francisco. The same applies to 3 radians which runs parallel to San Francisco. Therefore, the answer has to be 4 radians or 229.2 degrees. The lines drawn below are only approximations, so are not pinpoint. 4 radians or 229.2 degrees passes over San Francisco somewhere in the vicinity of the airport - but this isn't the answer. If we add back the magnetic north value of 17 degrees in 1970, it equals 246.2 degrees. After all, Zodiac stated on the map, it was "to be set to Mag.N." 
How do we know 246.2 degrees is the correct angle to be subtended from Mount Diablo? The answer is simple - Zodiac told us so. Place the crosshairs above over a compass rose. A line subtended from the center of the compass rose passes exactly through the center of the bold black circle. In other words, the bold black circle is positioned at 246.2 degrees around the crosshairs. This is 4 radians + 17 degrees (magnetic north). Now all we have to do is find the inches subtended along the 246.2 degree line. This is even easier.     

The map scale is 6.4 miles to the inch, so the geography of San Francisco is self-constraining.
It is approximately 26.5 miles to the eastern edge of San Francisco from Mount Diablo (using the angle of 246.2 degrees).
4 inches would equal 25.6 miles, therefore, 4 inches subtended from Mount Diablo would land in the sea. Unless the Zodiac Killer had a submarine to bury his bomb this is not very likely.
It is approximately 34 miles to the western edge of San Francisco from Mount Diablo (using the angle of 246.2 degrees). 
6 inches would equal 38.4 miles and again would land in the sea.
Therefore, the answer has to be five inches along the 4th radian (plus magnetic north of 17 degrees). If this lands over the San Francisco Police Department we are in business. But first, we shall fill in the '32 Symbol' code using the words or clue given by the Zodiac Killer in the July 26th 1970 'Little List' letter.  
The section below is almost the complete solution to the '32 Symbol' cipher. Note how the Zodiac Killer inserts a hashtag style character between the "&" and "inches", with an arrow pointing between these two pieces of text. He is telling us to insert something here. We know from the above calculation it must be five inches, thereby completing the phrase:
"P.S The Mt.Diablo code concerns Radians & five inches along the radians"
​

The Zodiac Killer wasn't totally accurate, because the phrase should have read "P.S The Mt.Diablo code concerns Radians & five inches along the radian". The five inches to be subtended along the 4th radian (plus magnetic north) = 246.2 degrees. 
There are only three repeating characters in the code below, the triangle, the letter C and the letter O. With the inserted solution, these three characters are now represented by R, A, N, N, E and N. 

It was there in the Zodiac Killer's words all along; "The Mt.Diablo code concerns...... Radians & inches along the radian"
The last thing we have to do is place the large crosshairs with the black circle over the map of Mount Diablo, San Francisco and Vicinity. The location where the intended bomb was to be set should be 246.2 degrees and 5 inches subtended along a line drawn from Mount Diablo. It should also land over something to do with the San Francisco Police Department. Bearing in mind this was 1970 and the Zodiac Killer was using a ruler over a map, one eighth of an inch or so would be an acceptable margin of error, based on a map scale of 6.4 miles to the inch. The center and style of the black bold circle may be representative of a designer who intended the target to fall within this circle.  
There was no room on the map below, but we can see that if the superimposed crosshairs were expanded over the city of San Francisco, the center of the bold black circle subtended at 246.2 degrees for 5 inches would fall over the San Francisco Police Department at Ingleside Station. 
Ingleside Police Station is 31.06 miles from Mount Diablo. There are 6.4 miles to the inch. So Ingleside is 4.85 inches along the subtended angle of 246.2 degrees. Allowing for the leeway of crude measurement, this is 97% accurate in respect to 5 inches over the distance involved. This is why the Zodiac Killer placed SFPD next to the bold circle - it represented zero in mocking fashion, but more crucially, it represented the location of where the bomb was intended to be set - Ingleside Station or somewhere close by.              

Richard Radetich, the fallen officer, possibly referred to in the Zodiac Killer 'Button' letter was initially assigned to Ingleside Police Station, before moving to Park Station and eventually to Accident Investigation.

Footnote: What level of understanding the Zodiac Killer had regarding the concept of radians is unknown, but they are a counterclockwise value around the circumference of a circle. He placed his crosshairs over Mount Diablo, to which he added a sort of clock face, replacing the number twelve with a zero, stating it was "to be set to Mag.N". It can be shown that 4 radians and Magnetic North will fall within the bold, black circle he placed on his 'Little List' crosshairs. In addition, it can be shown that traveling 2 radians counterclockwise from True North will again fall within the bold, black circle. The use of the clock face and the directional north marker set at zero, may indicate that Zodiac intended this as his starting point for any calculations. The mere fact that the above measurements, either clockwise or counterclockwise, using whole radians, both fall inside the black circle, would seem to suggest that the 246 degree angle subtended from Mount Diablo over San Francisco is where we should be looking.​

The Zodiac Killer quoted a portion from one of the three stanzas of The Mikado's Tit-Willow, when he mailed the 'Exorcist' letter on January 29th 1974. This may possibly have been the third correspondence, including the 'Halloween' card, where The Mikado was referenced. The Zodiac Killer began with the 'Little List' letter on July 26th 1970, in which he paraphrased 'As some day it may happen' featuring Ko-Ko the Lord High Executioner. In the letter he was effectively quoting the search for future victims as paralleling his agenda throughout the state of California. If we break down the 'Exorcist' letter into its constituent parts, it becomes apparent the correspondence is a further threat towards the citizens of California rather than a declaration of his impending suicide.
If we take a look at the October 27th 1970 'Halloween' card and compare it to his confirmed attacks, only one stands out. On September 27th 1969 Cecelia Shepard and Bryan Hartnell were relaxing by the shores of Lake Berryessa when a man spotted by Cecelia ducked behind a tree to don an executioner's mask and waistline bib. This theatrical entrance in the form of Ko-Ko the Lord High Executioner has long been suggested as an influence on the Zodiac's actions and writings. Here is an extract from the San Francisco Chronicle on October 12th 1970, just 15 days prior to the mailing of the 'Halloween' card:
"It was immediately apparent that Zodiac had plagiarized several stanzas from an aria in the Gilbert and Sullivan operetta 'The Mikado'. It is the entrance aria of Ko-Ko, the Lord High Executioner. A quiet search of onetime Ko-Ko's has turned up none that could be Zodiac. Obvious differences in physical description and handwriting comparisons have cleared all Ko-Ko's tracked down since the arrival of the July 27 letters." 

The 'Halloween' card depicted an eye peering from the knothole of a tree, accompanied by the words 'peek-a-boo you are doomed', implying the impending threat of the Zodiac Killer hiding behind the tree at Lake Berryessa and his ultimate arrival bedecked in an executioner's outfit. If you look up the definition of peek-a-boo in Wikipedia, it quotes "Peekaboo (also spelled peek-a-boo) is a form of play primarily played with an infant. To play, one player hides their face, pops back into the view of the other, and says Peekaboo!, sometimes followed by I see you! There are many variations: for example, where trees are involved, "Hiding behind that tree!" is sometimes added." 
However, Peek-A- Boo was also a character in another version of The Mikado at around the same time as the Gilbert and Sullivan operetta. "In 1888 Jack the Ripper terrorized the Whitechapel district of London. In the same year of somewhat less significance Ed J. Smith wrote a stage parody called The Capitalist; or, The City of Fort Worth. Designed to encourage capital investment in Fort Worth, Texas, and underwritten by local banks and railroad lines, the two act piece features characters named Yankee-Doo, Kokonut, By-Gum and Peek-A-Boo." Here is an image depicting this reference.     

Peep-bo is the English version of peek-a-boo, and has a curious, albeit likely unintentional connection to the Lake Berryessa murder of Cecelia Shepard, in the nursery rhyme Little Bo-Peep.
​"The earliest record of this rhyme is in a manuscript of around 1805, which contains only the first verse. There are references to a children's game called "bo-peep", from the 16th century, including one in Shakespeare's King Lear (Act I Scene iv), for which "bo-peep" is thought to refer to the children's game of peek-a-boo, but no evidence that the rhyme existed earlier than the 18th century. The additional verses are first recorded in the earliest printed version in a version of Gammer Gurton's Garland or The Nursery Parnassus in 1810". Wikipedia.
Peep-bo was one of the three little maids from The Mikado: "Three little maids from school are we, pert as a school-girl well can be, filled to the brim with girlish glee, three little maids from school." 

Three young girls from Pacific Union College would feature in the Zodiac story of Lake Berryessa that day, when describing a suspicious individual roaming the hillsides surrounding the lake- later providing a sketch of the individual. 
Little Bo-Peep was a shepherdess, so its significance to the name of Cecelia Shepard could not be ignored, although likely accidental. "She heaved a sigh and wiped her eye, and over the hillocks went rambling, and tried what she could, as a shepherdess should, to tack each again to its lambkin"
The Riverside murder of Cheri Jo Bates on October 30th 1966 and the subsequent 'Confession' letter held an odd precursor to the events of Lake Berryessa, when it stated "Miss Bates was stupid. She went to the slaughter like a lamb", along with the widely referenced "She squirmed and shook as I choked her, and her lips twitched" connection to the 'Little List' letter.  

​The Zodiac Killer, after mailing his response to the unearthed Riverside connection would then go into hibernation from March 13th 1971 until the arrival of the 'Exorcist' letter nearly three years later on January 29th 1974, leading many to believe the Zodiac Killer was likely incarcerated during this period. 
"Taken from the county jail
By a set of curious chances;
Liberated then on bail,
On my own recognizances;
Wafted by a favouring gale
As one sometimes is in trances,
To a height that few can scale."  Behold the Lord High Executioner Youtube
The Mikado/Act I/Part V
The Lord High Executioner was to return, berating the 1973 film 'The Exorcist,' yet curiously comparing it to the Gilbert and Sullivan's satirical operatic comedy, The Mikado, calling it "the best satirical comedy that I have ever seen."  He then signed his name using the verse of Tit-Willow by Ko-Ko: "He plunged himself into the billowy wave and an echo arose from the suicides grave, titwillo, titwillo, titwillo."
The whole letter was effectively announcing the return of the Lord High Executioner after nearly three years. Here is the 'Exorcist' letter broken down into its constituent parts to reveal its likely meaning.
"I saw and think "The Exorcist" was the best satirical comedy that I have ever seen, even better than The Mikado. Signed, yours truley: The Lord High Executioner. If I do not see this note in your paper, I will do something nasty, which you know I'm capable of doing- To Kill."
Kevin Robert Brooks came up with possibly the best interpretation of the Japanese/Asian symbols at the foot of the letter, befitting of Ko-Ko the Lord High Executioner. The "This is the Zodiac speaking" introduction was apparent by its absence, as well as the Zodiac crosshairs- but the Lord High Executioner was alive and well, and still making threats.  

The Zodiac Killer teased us with his name on more than one occasion, firstly in the July 31st 1969 San Francisco Chronicle letter where he stated "I want you to print this cipher on the front page of your paper. In this cipher is my idenity." He would follow this up with the 'My Name is...' letter on April 20th 1970 and the 'Halloween' card on October 27th 1970 tempting us with his name again; "I feel it in my bones, You ache to know my name, And so I'll clue you in.." 
​It would appear however, this was never to be the case and we are still no nearer to securing the identity of the Zodiac Killer nearly half a century later. It always seemed strange the Zodiac Killer would interpose the Gilbert and Sullivan Mikado into his correspondence, leading researchers to believe he was a fan of the theater, having quoted three acts of The Mikado in the 'Little List' letter of July 26th 1970 and 'Exorcist' letter of January 29th 1974. But there may be an ulterior motive behind this apparent fascination with Gilbert and Sullivan, in that the killer was using the Mikado to reveal his name, and likely through four mailings rather than the accepted two. We will take a closer look at these four correspondences and the speculative links between them, without claiming this is anything more than coincidence. Let us first look at the 'Exorcist' letter.   

The first thing to notice is its carefully structured appearance, being divided neatly into four sections of text. The curious thing about the correspondence is Zodiac wrote "Signed, yours truley," as though he was about to offer up his name in the third block of writing. He then recited ​Act II -On a tree by a river from The Mikado. It seemed like Zodiac was wasting our time, plucking out random verses from The Mikado, that is until you read verse three of this particular act. It not only contained a reference to 'name', but pointed us towards 'The My Name is...' cipher, mailed on April 20th 1970. Here is verse three.
Now I feel just as sure as I'm sure that my name
Isn't Willow, titwillow, titwillow,
That 'twas blighted affection that made him exclaim
"Oh, willow, titwillow, titwillow!"
And if you remain callous and obdurate, I
Shall perish as he did, and you will know why,
Though I probably shall not exclaim as I die,
"Oh, willow, titwillow, titwillow!"

Was the Zodiac Killer giving us clues to his identity or name, by leading us back to the '13 Symbol' cipher. This observation on its own is meaningless, so we will travel back in time to the 'Little List' letter mailed on July 26th 1970, the supposed only other correspondence to contain references to The Mikado- in fact two. The first section of the 'Little List' letter pulled lines from  'A more humane Mikado', and continued on to extensively recite Gilbert and Sullivan's Mikado Act One Part 5a  'As some day it may happen', performed by Ko-Ko. In the introductory part of the letter, Zodiac simply boasted about how he would torture his slaves in paradise, but he again did something curious, by selecting just one small section of 'A more humane Mikado,' despite it being ten verses in length. The same as he did in the 'Exorcist' letter. He then continued to paraphrase the entirety of 'As some day it may happen'.
The 'Exorcist' letter, we have shown to have tenuous links to the April 20th 1970 'My Name is...' letter, using verse three of 'Tit-Willow'. So let us look at the small section of text Zodiac selected from 'A more humane Mikado.'
The 'Little List' letter read "And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes."  Why does Zodiac select this small portion. Was this also hinting towards the 'My Name is...' cipher.
When we think of billiard players or billiard balls from the standpoint of America, eight-ball comes to mind, and the circled eights on the '13 Symbol' cipher. 

This is the full verse (right) from 'A more humane Mikado.' It is actually verse eight out of ten, providing us with the numerical link, as did verse three from the 'Exorcist' letter. The Zodiac Killer did state on the 'My Name is...' letter; "PS I hope you have fun trying to figgure out who I killed."​​​
There is however another link from 'A more humane Mikado,' to the alphabetical characters on the '13 Symbol' code mailed by Zodiac.
The Zodiac Killer supplied us with eight alphabetical characters, reading from left to right  A, E, N, K, M, N, A and M.
In the diagram below, key sections of 'A more humane Mikado' are highlighted for comparison to the '13 Symbol' cipher. Seven letters have been highlighted in green and yellow. This is where we must take a bold leap of faith, and consider that the Zodiac Killer chose The Mikado by Gilbert and Sullivan because it simply contained his name, Kim. Nothing more theatrical than that. 

The green highlighted sections on 'A more humane Mikado' in reverse, read KIMNAM. If we believe therefore, that the middle eight represents the letter I on the '13 Symbol' cipher, it reads forward KIMNAM, exactly the same. The remaining letters of the cipher AEN are shown highlighted in yellow. Every letter on the '13 Symbol' cipher is contained within this section of seven letters. 
​The three eights encapsulated his identity, just like the three eights at the foot of the '340' character cipher mailed on November 8th 1969: The Mathematics of the 13 Symbol Cipher. Who said the Magic 8 ball was just for telling fortunes! Additionally, Mikado can be formed using the alphabetical characters on the 20th line of the '340' cipher.
The Zodiac was keen to share with us what he had in store for his slaves in paradise:
"This is the Zodiac speaking. Being that you will not wear some nice buttons, how about wearing some nasty buttons. Or any kind of buttons that you can think up. If you do not wear any type of buttons, I shall (on top of everything else) torture all 13 of my slaves that I have waiting for me in Paradice. Some I shall tie over ant hills and watch them scream + twich and squirm. Others shall have pine splinters driven under their nails + then burned. Others shall be placed in cages + fed salt beef untill they are gorged then I shall listen to their pleass for water and I shall laugh at them. Others will hang by their thumbs + burn in the sun then I will rub them down with deep heat to warm them up. Others I shall skin them alive + let them run around screaming. And all billiard players I shall have them play in a darkened dungen cell with crooked cues + Twisted Shoes. Yes I shall have great fun inflicting the most delicious of pain to my slaves."
The talk of slaves, paradise, pine splinters, dungeons and hanging his 'prisoners' by the thumbs, catapulted me to the 'Halloween' card mailed on October 27th 1970, and the last Mikado installment. The Zodiac Killer placed some wording around the knothole in the tree:"peek a boo you are doomed." Bearing in mind that The Mikado opened to the paying public on March 14th 1885, and was hugely successful, running for 672 performances at the Savoy Theatre in London, a British connection had to be sought. The British term for peek-a-boo is peep-bo, and peep-bo is a character in The Mikado.      

In analyzing the 'Button' letter map and code mailed on June 26th 1970, it is imperative we take a close look at the Zodiac Killer correspondence in the preceding few months to this communication for any clues to his mindset and intentions. There will be no definitive solution to the 32 symbol code presented here, although a location for where his bomb was 'to be set' can be argued with confidence, using four pieces of Zodiac material.
On April 20th 1970 the killer mailed 'The My Name is..Cipher' and stated "I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station.  Even though I talked about killing school children with one. It just wouldn't doo to move in on someone else's teritory.  But there is more glory in killing a cop than a cid because a cop can shoot back." The Zodiac Killer was referring to the murder of San Francisco police officer Brian McDonnell on February 16th 1970, two months earlier, when a bomb exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. See here. 
He would back up this correspondence with the 'Dragon Card' just one week later on April 28th 1970 declaring "I hope you enjoy yourselves when I have my blast." This card featured elements of the book Don Quixote, a novel by Miguel de Cervantes Saavedra, in which Alonso Quijana, a prolific reader of books, became so mesmerized by the chivalry contained within them, that under the assumed name of Don Quixote, along with his squire Sancho Panza, began a quest to revive this virtue. What the Zodiac Killer was inferring with this particular card can be debated, but the 1899 Waller Street Police Station is situated on the boundary of the San Francisco Golden Gate Park and in close proximity, also situated in the park, is the memorial statue of Miguel de Cervantes, featuring Don Quixote and Sancho Panza. Was the Zodiac Killer insinuating an attack close to the police station and park, similar to the murder of police officer Brian McDonnell.  

Then on June 26th 1970 this communication arrived, insinuating the murder of another police officer, Richard Radetich (25). On June 19th at 5.25 am he was gunned down by three shots from a .38 caliber revolver at point blank range through the driver side window of his vehicle, while in the process of serving a parking ticket by 643 Waller Street, San Francisco, in the Lower Haight District and subsequently died 15 hours later. The murder of Richard Radetich, as of writing, remains unsolved.
​The Zodiac Killer appeared to be heavily centering his focus in the Haight District. The statue in the park, 1899 Waller Street and 643 Waller Street all fall within a 2 mile radius, featured through three consecutive mailings.
It is therefore this locality of San Francisco we shall again turn our attention to, when considering where the Zodiac Killer may be directing his threat towards in the Button letter, using recent history to predict the future.
There is good reason to believe the Zodiac Killer was threatening an attack on Ingleside Station-San Francisco Police Department, located at 1 Sgt John V Young Lane, named in honor of Sgt. John Young, killed by gunmen in 1971 after they stormed the police station. Ingleside Station is 4.6 miles south of 1899 Waller Street. The Zodiac Killer never followed through on many of his claims, but this may very well be the location he was threatening to bomb on June 26th 1970. So here is the evidence.
When the Zodiac Killer mailed the Button letter, it was accompanied by a Phillips 66 road map and his crosshairs, stating they were "to be set to Mag.N." That is magnetic north, calculated at 17 degrees in 1970. Clearly he soon realized that the information or code he supplied, coupled with the Phillips 66 map, was insufficient to crack the cipher or determine a location for the bomb. One month later he rectified the problem with the Little List letter mailed on July 26th 1970, when he incorporated two further crosshairs, with all the clues we needed.     

This was the first crosshair on the right.
The Zodiac Killer continually taunted police with his running victim total, always attributing the police with zero. This was nothing new. However here he deliberately brings attention to the zero, marking it noticeably darker, as though it has increased significance. It is also placed within the crosshairs, indicating an area within his sights.
Bearing in mind the acronym SFPD, it is clear he has the San Francisco Police Department firmly focused as his target. That police department, we will attempt to show, was Ingleside Station located just off Balboa Park at San Jose Avenue.
The Zodiac Killer sent us a second set of crosshairs in the Little List letter stating "PS. The Mt Diablo code concerns Radians + inches along the radians."
This was the clue we needed.
In a previous article we highlighted a region of San Francisco for particular interest, using the following technique, but with improved map plotting and examining carefully the Phillips 66 map, it has become apparent the amended focus should be squarely over Ingleside Police Station.
The phrase "PS. The Mt Diablo code concerns Radians + inches along the radians," clearly tells us to use radians as our degrees from the north axis and is "to be set to Mag.N."  So we are looking for whole radians, to which we then add in the magnetic north value of 17 degrees. This will give us our angle on the Phillips 66 map.
The​ bold circle above is sitting between the 180 and 270 degree axis. In fact the center of the bold circle is positioned at 246 degrees. This can be confirmed using a compass rose. One radian is valued at 57.296 degrees, so four radians are valued at 4 X 57.296 = 229.184 degrees. Add in the magnetic north value of 17 degrees and our final total is 246.184 degrees.
The Zodiac Killer was indicating four radians + magnetic north. He never incorporated this into the Button letter code and Phillips 66 map, telling us the crosshair was to be set to magnetic north, but a month later in the Little List letter, he added the magnetic north value in for us, seen by the positioning of the bold circle next to SFPD. Four radians and 17 degrees is 246 degrees. This bold circle is also positioned at exactly 246 degrees (see below). 

This compass rose and SFPD crosshair, angled at 246 degrees can now be placed over the Phillips 66 map. But first we will examine the second  crosshair placed at the foot of the Little List letter.
The Zodiac Killer placed 'Diablo', the Spanish word for devil over the 180 degree axis. This may not have any significance, but if we couple the 66 from Phillips 66, with the number 6 on the Phillips map crosshair, we get 666, the number of the beast. By using the same method we can add the number 66 to the 180 degrees and arrive at 180 + 66 = 246 degrees once more.
Whether this was by design however, is open to question.
Let us now go ahead and superimpose the compass rose and SFPD crosshair over the Phillips 66 map (below).
To be completely accurate, both have been tilted by three degrees to match the original Zodiac crosshair. (shown here).
246 degrees takes us, as the crow flies, 31 miles southwest, passing directly over Ingleside Station-San Francisco Police Department (SFPD). The map scale is 6.4 miles to the inch, so if we were traveling inches along the radians, it would be 4.84 inches.  
If we round off, the phrase "PS. The Mt Diablo code concerns Radians + inches along the radians," would become: "PS. The Mt Diablo code concerns four Radians + five inches along the radians." That is 229 degrees, but set to magnetic north gives us the 246 degrees shown in the diagrams. 

The Button letter code however, as mentioned above, would not incorporate the exact angle or directions to Ingleside Station. Remember the Zodiac Killer stated "The Map coupled with this code will tell you where the bomb is set."
The map crosshair told us to "set to Mag. N", which was 17 degrees. So if the code had an angle within it, this angle would be 229 degrees (before it is coupled with the map).
With 29 unique characters in the 32 symbol code, simple substitution is not an option. Some form of key must be unearthed.
Below are two incorrect examples of what we may be looking for. The first example matches all the repeating characters, even the dotted circle, but makes no sense. The second is more recognizable as a logical sentence, but matches little within the code. You may have a better solution. 
Ingleside Police Station may very well have been the target of the Zodiac Killer, but without breaking the code, it will remain a possibility rather than a proven fact. Thank you for your time. 

In a recent article we examined the Mount Diablo code in conjunction with the Phillips 66 road map and suggested a possibility that the Zodiac 32 Symbol cipher may have revealed San Francisco International Airport, situated at 4 radians or 229 degrees from Mount Diablo. However,  coupled with the Magnetic North value of 17 degrees at the time of mailing, was to give us a final value of 246 degrees, exactly corresponding with the bold circle the Zodiac Killer provided within his crosshairs on the 'Little List' letter mailed on July 26th 1970.  View initial article (Part One). View Part Two.
This final part of the trilogy will attempt to cement the motivation behind the Zodiac Killer's crosshairs, which he gave us on the Phillips 66 road map (as part of the Button Letter) mailed on June 26th 1970 and the 'Little List' letter one month later on July 26th 1970. In the following diagram we have incorporated the three crosshairs together to better explain the findings. This idea has been covered before, but finalizes the three part story under one banner in a little more detail.

The Zodiac Killer stated on the Button letter "The Map coupled with this code will tell you where the bomb is set". In other words, the two are to be used in conjunction with each other. This is what we did in the earlier articles, taking the code of San Francisco International Airport at 229 degrees and coupling it with the map, set at a Magnetic North value of 17 degrees, to arrive at the final value of 246 degrees.
However, this would not have been possible using the Button letter and Phillips 66 road map alone. The Zodiac Killer realizing this, gave us the two additional crosshairs on the Little List Letter, with a couple more hints. Firstly, the bold circle and secondly the phrase "PS The Mt Diablo code concerns Radians + inches along the radians". The Zodiac Killer placed this phrase over the crosshairs itself, when he could have easily accommodated both elements separately - unless of course he had an ulterior motive.

The phrase "PS The Mt Diablo code concerns Radians + inches along the radians" runs over the south axis; or to be precise, over the 180 degree axis or number 6 on the Zodiac dial. The only word bisected by this south axis is​ Diablo. 
Let us expand upon the "Map coupled with this code will tell you where the bomb is set" to better explain things, using this phrase "The Phillips 66 Map coupled with this code will tell you where the bomb is set". In the first instance, the code of San Francisco International Airport or 229 degrees was coupled with the map set to Magnetic North of 17 degrees, to equal 246 degrees. The 'Mount Diablo code' was written on the 180 degree axis, so we will couple this 180 degrees with the map (or more specifically the Phillips 66 map), to give us 180 + 66 = 246 degrees, the exact position of the bold circle he provided us in the 'Little List' letter and exactly the same as 4 radians and 17 degrees. Then we shall take the number 6 he provided on the 180 degree axis and once again couple this with the Phillips 66 map to give us 666, the mark of the Devil or Diablo.

The conventional view is that the Mount Diablo peak derives its name from the 1805 escape of several Chupcan Native Americans from the Spanish in a nearby willow thicket. The natives seemed to disappear, and the Spanish soldiers thus gave the area the name "Monte del Diablo", meaning "thicket of the devil." Diablo was placed over the 180 degree mark and the number 6 axis, and on both occasions coupled with the 66 from the Phillips 66 road map, it gave us something significant. But whether or not this was his true intention is still unclear and may never be resolved. 

Footnote: What level of understanding the Zodiac Killer had regarding the concept of radians is unknown, but they are a counterclockwise value around the circumference of a circle. He placed his crosshairs over Mount Diablo, to which he added a sort of clock face, replacing the number twelve with a zero, stating it was "to be set to Mag.N". It can be shown that 4 radians and Magnetic North will fall within the bold, black circle he placed on his 'Little List' crosshairs. In addition, it can be shown that traveling 2 radians counterclockwise from True North will again fall within the bold, black circle. The use of the clock face and the directional north marker set at zero, may indicate that Zodiac intended this as his starting point for any calculations. The mere fact that the above measurements, either clockwise or counterclockwise, using whole radians, both fall inside the black circle, would seem to suggest that the 246 degree angle subtended from Mount Diablo over San Francisco is where we should be looking.​