Professor D.C.B. Marsh told the San Francisco Examiner on October 22nd 1969: "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allan Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name - in cipher code - would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code - however complicated - which will truly and honestly include his name".

​The Zodiac Killer responded on November 8th 1969 by using the scytale method of decryption featured at the top of Poe's essay A Few Words On Secret Writing. Or should I say, it can be used to crack the 340 cipher encrypted message, that contained the wording "one in paradice" just like Edgar Allen Poe's poem to his dead wife entitled "To One In Paradise". The next method of encryption in Poe's A Few Words On Secret Writing involved splitting the alphabet A to M and N to Z (two sections of thirteen) mirroring the Zodiac's 13 character code which began with A and ended with M - and because of the distinct lack of characters in this code - it has been considered unsolvable using standard cryptographic methods.

​The Zodiac seemingly didn't supply us with a key to this code in later communications, leading me to believe that the key or answer lies in the Edgar Allen Poe essay mentioned above. I believe the answer to the code is ​"This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....Fk, I'm crackproof, in which each element of the phrase is begun by each of the circled eights, thereby creating an infinite circular cipher (hence the circled 8's which represent infinity and a new beginning). The Zodiac Killer may have supplied us with the answer to the Z13 code in the 13-Hole postcard on October 5th 1970 in which he configured the punched holes in an arrangement of 10 to 3, pinpointing the position of the three eights, and supplying the answer of Fk, I'm crackproof. Using Edgar Allen Poe's reasoning in A Few Words On Secret Writing, I can now place five letters in the correct position within the 13 character code, albeit not to my complete satisfaction.  

Here is a section of reasoning from Edgar Allen Poe's A Few Words On Secret Writing where A can represent N and vice versa, where B can represent O and vice versa, and where C can represent P and vice versa. But he also makes a point of saying A might stand for P (or vice vera). This is where I shall jump into the code using a trial and error approach. 

If A can stand for P, I shall place P above the A in the beginning of the Z13 code like so:

If A can stand for P, and P can also represent C, then A can also stand for C. So let us insert the letter C above A in the Z13 code.

If A can represent N and vice versa, B can represent O and vice versa, and C can represent P and vice versa, then E can represented R. So let us place R in the Z13 code.

Edgar Allen Poe stated that N can represent A, so let us place A above the second N in the Z13 code:

If A can stand for P, and P can also represent C, then A can also stand for C. This means that if M can stand for X, and X can represent K, then M can also stand for K (just like A stood for C). So let us insert K into the Z13 code:

If the K and M between the three eights are representative of themselves as I have previously surmised, then we have the beginning of the answer to the Z13 code. But without this assumption, we have five letters inserted that mirror the previous solution I have suggested - all reasoned from Edgar Allen Poe's essay. It's not perfect, but it's a start.

Just over two weeks before the 340 cipher was mailed, Dr. D.C.B. Marsh of the American Cryptogram Association laid down a challenge to the Zodiac in the newspapers to reveal his name in a cipher, however complicated. The wording in the San Francisco Examiner on October 22nd 1969 invoked the name of Edgar Allan Poe, so possibly the designers of the article were hoping that the Zodiac Killer would invoke Edgar Allan Poe to give us his name, making any offering easier to crack. This appeared to influence the Zodiac Killer, because the first cipher mentioned in Poe's essay A Few Words on Secret Writing actually works in decoding the message in the 340 cipher. The second cipher technique in Poe's essay A Few Words on Secret Writing split the alphabet into two portions of 13 letters, so it was surprising that the Zodiac Killer's next code reduced dramatically to 13 characters just like Poe's design (beginning with A and ending with M). See here for essay.

Three years ago, it was suggested that the Zodiac Killer wouldn't again shy away from the challenge of giving us his name, having possibly given us it in an abbreviated format. That is why the cryptic reference of Fk, I'm crackproof caught my eye in the October 5th 1970 communication with 13 punch-holes in the fabric of the card. The punch-holes were separated into a 10 to 3 configuration, positioned in such a way that they mirrored the design of the 13-Symbol cipher. The only way to break the small code was to discover the entry point, and the three circled 8's seemed as good a place as any, especially when we consider Fk, I'm crackproof is split into three parts and fits around the existing K and M in the code. The crosshairs, anchor and Celtic Cross in the code are all religious symbols, with the number 8 representing rebirth, regeneration and a new beginning in Christianity. The figure 888 is also representative of Jesus Christ in Christian numerology. It was discovered that the first 8 began FK, the second 8 began IM and the third 8 began CRACKPROOF, which completed the circle of eternal life. The introduction to the April 20th 1970 letter was also completed, to "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof",

Anyway, this is to show that the Fk, I'm crackproof solution was found before the 340 cipher was cracked by Dave Oranchak, Sam Blake and Jarl Van Eycke on December 3rd 2020, along with its scytale links to Edgar Allan Poe's A Few Words on Secret Writing. This is extremely important when we consider the following. Edgar Allan Poe highlighted certain encipherment techniques in the essay regarding a split alphabet, which are outlined here: and, so placed, a might stand for n and n for a, o for b and b for o, &c. &c. This, again, having an air of regularity which might be fathomed, the key alphabet might be constructed absolutely at random. The next line was: Thus A might stand for P.

These examples can be summarized as;
[1] a might stand for n and n for a
[2] Therefore, r might stand for e and e for r
[3] Thus, a might stand for p (and vice-versa)
Using only these examples in the 13-Symbol cipher, I inserted the possibilities into the code, using the letters K and M as entry points, based on the aforementioned reasoning. The letters N, A and M (not boxed in blue) I have no explanation for. So the search goes on to discover whether the Zodiac applied something else to the encryption. Or whether a different technique was used entirely.

When you take into consideration that the Fk, I'm crackproof solution was suggested in 2017, before the scytale link of the 340 cipher to Edgar Allan Poe, coupled with the formation above using just Poe's examples shown in [1], [2] and [3], it shows a pattern receptive to the remaining letters in the solution. But the three remaining ciphertext characters would need explaining. 

The next encipherment technique described in A Few Words on Secret Writing were the two concentric circles (one fixed), where the outer wheel can be rotated around the inner wheel during the coding process. Here is a working cipher wheel.

On October 22nd 1969, Dr. D.C.B Marsh in alliance with investigators and the San Francisco Examiner, attempted to refocus the Zodiac Killer's attention toward creating a second major cryptogram and "reveal his name in the cipher to established cryptogram experts". Marsh would continue to press the killer throughout the article, stating "I invite Zodiac to send to The American Cryptogram Association a cipher code - however complicated - which will truly and honestly include his name". However, in order to crack any cipher the killer may send, it would have been wise to place certain triggers within the article to guide the Zodiac Killer into choosing a particular cryptographic technique. This may have been the purpose of dropping the name Edgar Allan Poe into the San Francisco Examiner article, thereby influencing the killer to choose a cryptographic technique highlighted by Poe in one of his essays. If the Zodiac Killer then responds with a second cipher, your first port of call would obviously be Edgar Allan Poe.

Although Dave Oranchak doesn't believe the Zodiac Killer used the scytale method of encryption in the recently decoded 340 cipher, this decryption tool does actually decode the message in the 340 cipher. If the Zodiac Killer responded to the prompt by Dr. Marsh and read Edgar Allan Poe's essay A Few Words on Secret Writing, he would have noticed that the first topic of discussion was the scytale cipher, which involves disguising a message by separation, avoiding the common left-to-right method of decryption. This is what the Zodiac Killer used in his 340 cipher. In further reading of A Few Words on Secret Writing, it became apparent that other encryption methods were discussed in addition to the scytale method, with the possibility existing that the Zodiac Killer may have adopted one of these techniques for his following 13-Symbol cipher on April 20th 1970. The most notable encryption methods discussed included separating the alphabet A to M, and N to Z, into two equal parts of 13 letters. This involved placing the alphabet into the following configuration.

Here is an excerpt from Edgar Allan Poe's A Few Words on Secret Writing: and, so placed, a might stand for n and n for a, o for b and b for o, &c. &c. This, again, having an air of regularity which might be fathomed, the key alphabet might be constructed absolutely at random. The next line was: Thus A might stand for P.

If we then represent the second ciphertext character N (11th position} with the plaintext character A shown in Poe's writing, we get the diagram shown below, with the circular Fk, I'm crackproof starting to emerge.

The relationship  between the remaining ciphertext characters of N, A and M, to the plaintext characters in the solution of O, C and K respectively, can be seen in the diagram below. These are never more than two apart in the alphabet. This is a work in progress.

The discovery of the message in the 340 cipher has triggered a new debate on the intelligence of the Zodiac Killer, bearing in mind the greater complexity of the encryption used to disguise its contents. Creating an extremely difficult cipher is actually far easier than attempting to decode it, especially when the person who designs the cipher accidentally bakes errors into his cipher as shown by the Zodiac Killer.

However, Cragle on the Zodiac Killer Site forum made an astute observation regarding the Zodiac Killer's switch from describing his hidden messages as ciphers, to codes in the June 26th 1970 and July 26th 1970 letters. While not completely true, because the Zodiac Killer stated "By the way, are the police having a good time with the code?" on August 4th 1969, it does open up the broader point of the difference between codes and ciphers, which is effectively what Cragle was implying. Codes generally operate on semantics, while ciphers operate on syntax. A cipher is a system to make a word or message secret by changing or rearranging the letters in the message, whereas a code is a system of changing entire words or phrases into something else. Codes are not just secret messages, they can be any symbol or signal used to represent, or communicate, something else.

One could argue, that if the Zodiac Killer invested the time to construct a period nineteen cipher, then he was certainly aware that by creating the Z13 and Z32  codes of such brevity and variability, he was effectively creating an impossible task and any realistic possibility of a solution without ultimately providing a key to each code. The fact that the Mount Diablo code had 29 unique characters in a 32 character array, makes it practically unsolvable without that key, A key explaining these 29 unique characters in his remaining communications appears not to be the case. The Zodiac Killer stated that "the map coupled with the code will tell you where the bomb is set", so if we take this literally, then the Zodiac Killer by June 26th 1970 expected us to solve the 32 character code with nothing more than the Phillips 66 map he supplied alongside the letter. He did supply additional clues on July 26th 1970 in the form of "P.S. The Mt. Diablo code concerns Radians + # inches along the radians", but as of June 26th 1970 he fully expected us to decipher these 29 unique characters with nothing more than a map, lending credence to the notion that this encryption was designed as a code rather than a cipher. Finding corresponding alphabetical letters to 29 unique characters appears an unlikely proposition with the limited information he provided. A man with the patience to design the 340 cipher encryption must have known this.

Sam Blake, who contributed to the solving of the 340 cipher, made an extremely valid point when stating that the decoded message was contemporary. By the Zodiac Killer claiming that "it wasn't me on the TV show", he fully expected his 340 cipher to be decoded fairly quickly. This message was for the moment, not for 51 years later. The same is probably true for the Z13 and Z32. These codes were apparently designed with the promise of a hidden name and bomb at a time when newspapers were king. When the Zodiac Killer started fading from the newspaper headlines by 1971, the ongoing quest to decipher these two codes had equally faded into obscurity. This isn't the case today, with the internet endlessly keeping the mystery and speculation alive. But as the 1970s rolled forward these codes would have faded from the publics gaze, making these puzzles much more contemporary at the time they were designed. The Zodiac Killer could enjoy the speculation surrounding his unsolved puzzles and codes while they were still being discussed in the newspapers, but once the San Francisco Chronicle and San Francisco Examiner have moved away from featuring the Zodiac Killer, the feedback surrounding his unsolved codes would equally fade away. He probably expected these two codes to remain unbroken for a limited time only.

Therefore, as Cragle intimated, we might be better rewarded by looking at the Z13 and Z32 codes through the lens of codes rather than ciphers. The search for words or phrases, in accompaniment to the limited clues he supplied, quite possibly a much more profitable avenue to go down. The solving of the 340 cipher has inevitably switched the focus of attention toward the remaining unbroken codes, with every effort being made to follow up on the success of Dave Oranchak, Sam Blake and Jarl Van Eycke. However, adopting an approach using cipher-type encryption may possibly lead to another 51 years of blind alleyways and false beliefs, scattered with the graveyards of "solved solutions" that never were.

After two Zodiac attacks in close succession on September 27th 1969 and October 11th 1969, investigators must have feared an escalation in terror from the Bay Area murderer, so it would have certainly been in their interests to switch the Zodiac Killer's attention to communication instead of murder. On October 22nd 1969, Dr. D.C.B Marsh in alliance with investigators and the San Francisco Examiner, attempted to refocus the Zodiac Killer's attention toward creating a second major cryptogram and "reveal his name in the cipher to established cryptogram experts". Marsh would continue to press the killer throughout the article, stating "I invite Zodiac to send to The American Cryptogram Association a cipher code - however complicated - which will truly and honestly include his name". However, in order to crack any cipher the killer may send, it would have been wise to place certain triggers within the article to guide the Zodiac Killer into choosing a particular cryptographic technique. This may have been the purpose of dropping the name Edgar Allan Poe into the San Francisco Examiner article, thereby influencing the killer to choose a cryptographic technique highlighted by Poe in one of his essays. If the Zodiac Killer then responds with a second cipher, your first port of call would obviously be Edgar Allan Poe.

Although Dave Oranchak doesn't believe the Zodiac Killer used the scytale method of encryption in the recently decoded 340 cipher, this decryption tool does actually decode the message in the 340 cipher. If the Zodiac Killer responded to the prompt by Dr. Marsh and read Edgar Allan Poe's essay A Few Words on Secret Writing, he would have noticed that the first topic of discussion was the scytale cipher, which involves disguising a message by separation, avoiding the common left-to-right method of decryption. This is what the Zodiac Killer used in his 340 cipher. In further reading of A Few Words on Secret Writing, it became apparent that other encryption methods were discussed in addition to the scytale method, with the possibility existing that the Zodiac Killer may have adopted one of these techniques for his following 13-Symbol cipher on April 20th 1970. The most notable encryption methods discussed included separating the alphabet A to M, and N to Z, into two equal parts of 13 letters. Followed by a technique involving two concentric discs, akin to the Union Cipher Disk that held the number configurations of 000 and 888. These techniques show promise when we consider the design and structure of the 13-Symbol cipher. This has been covered in a much more extensive article, so it will not be covered any further here.  

Dr. Marsh, under the banner of Cipher Expert Dares Zodiac to Tell Name, would persist throughout the article into cajoling the Zodiac Killer to reveal his name by way of a cryptogram. This is why another passage in A Few Words on Secret Writing caught my attention - and may have resonated with the Zodiac Killer too. It concerned a reader sending in cryptograms to Edgar Allan Poe, but refraining from giving his name. The passage read "This challenge has elicited but a single response, which is embraced in the following letter. The only quarrel we have with the epistle, is that its writer has declined giving us his name in full. We beg that he will take an early opportunity of doing this, and thus relieve us of the chance of that suspicion which was attached to the cryptography of the weekly journal above-mentioned–the suspicion of inditing ciphers to ourselves. The postmark of the letter is Stonington, Conn".

This reminded me of the statement by Dr. Marsh when he challenged Zodiac, who he contended "had not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald". He claimed "Zodiac has not done this, because to tell the complete truth in relation to his name would lead to his capture". Did the Zodiac Killer read this passage in A Few Words on Secret Writing and get some ideas?

The reader who mailed Edgar Allan Poe from Stonington, Connecticut, failed to supply his name, but did begin by placing a letter S, followed by a horizontal dash, similar to the Zodiac Killer's introduction on April 20th 1970, The Zodiac Killer began the introduction to his 13-Symbol cipher by stating MY NAME IS ---------. The sender of the cryptograms to Poe only signed his name at the bottom of the intoductory letter by use of initials, concluding with "I am yours, respectfully S.D.L." Not wanting to shy away from the challenge of Dr. Marsh a second time, I couldn't help thinking that the Zodiac Killer may have rose to the challenge and given us the initials to his name (or fictitious initials), just like the sender of the cryptograms from Stonington, Connecticut. Another thing to note, is that Dr. Marsh laid down this challenge on October 22nd 1969, so 182 days had elapsed before the Zodiac Killer's third confirmed cryptogram arrived at the San Francisco Chronicle on April 21st 1970.

Paul Avery wrote on April 22nd 1970, in an article entitled Zodiac Sends New Letter-Claims Ten, that "the killer who calls himself Zodiac has once again written to the Chronicle. In a letter received yesterday, Zodiac claims he has killed again". This letter was received by the San Francisco Chronicle on April 21st 1970, the exact day and month the letter from Stonington, Connecticut was postmarked from the anonymous sender to Edgar Allan Poe. This all may have been coincidence, but it would certainly be worth looking for the Zodiac Killer's initials as part of the answer to the 13-Symbol cipher.

That answer could be "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof", given to us in the Zodiac Killer's postcard five-and-a-half months later as a big hint to its decipherment. The 340 character cipher was split into rows of 9, 9 and 2 sections. The 13-Symbol cipher may have been split into 2. 2 and 9 sections, with the circled 8's beginning each section of the phrase. The letters K and M were already in place for a perfectly circular message, as highlighted in the October 5th 1970 communication by the Zodiac Killer, in which he supplied us with the phrase Fk I'm crackproof.   

On April 20th 1970, the Zodiac Killer mailed a 13-Symbol cipher to the San Francisco Chronicle, in addition to a bus bomb diagram threatening to blow up a school bus. Let's compare the 13-Symbol cipher to the 13-Hole postcard on October 5th 1970, in which the Zodiac Killer may have completed the introduction of "My name is" to "My name is Fk, I'm crackproof", again teasing us with a less than complete resolution to his real identity.

On April 20th 1970, the Zodiac Killer made reference to the murder of San Francisco police officer Brian McDonnell (44) 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.  He wrote "I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station", while simultaneously giving us a diagram of a bomb to be placed just 274 feet from another "cop station", that of Ingleside. This sense of irony didn't seem lost on the Zodiac Killer. What the Zodiac Killer knew of Brian McDonnell, other than what he read in the intervening two months is unknown, but in the remainder of his short message he stated "But there is more glory in killing a cop than a cid because a cop can shoot back". Was this just an offhand comment, or was this statement relevant to the history of Sergeant Brian McDonnell?

The Desert Sun newspaper of February 17th 1970 read: Haight Ashbury Police Station Rocked By Bomb Six Officers Injured In Blast Showering Big U-Shaped Staples.

SAN FRANCISCO (UPI) - A powerful bomb packed with U-shaped staples rocked a Haight-Ashbury District police station Monday night injuring six policemen, one of them critically. New Police Chief A. Nelder said the fused explosive was placed on the rear window sill of the sergeant’s office at Park Station in Golden Gate Park. The thunderous blast, which jarred residents for blocks around, sprayed staples through the office like miniature machinegun bullets. Sgt. Brian McDonnell fell gravely wounded with multiple head injuries. Patrolmen Robert Fogerty, 43, and Frank Rath. 27, were hospitalized with multiple puncture wounds. Officers Alfred Arnaud, 24, Robert O’Sullivan, 26. and Ronald Martin, 28, were treated for lesser injuries. “All I remember was a bomb exploded,” said one shaken officer who survived with only scratches. “I saw Sergeant McDonnell lying in the rubble, bleeding from an artery wound in his neck.” Police immediately sealed off the area and rerouted traffic. First reports indicated the building had been demolished. The blast did knock out all power in the station and shattered every window. It also demolished the sergeant’s police station wagon which was parked behind the station near Kezar Stadium, where the San Francisco Forty Niners play National Football League opponents. There were reports that a man was seen running from the station, and police later said a white and pink van was sighted leaving the area. However, there were no immediate suspects. Four days ago, three cars were blown up and two reserve policemen were injured by two bombs which exploded in a parking lot adjacent to the Berkeley police station across the bay from San Francisco. The explosive used in the Berkeley bombing was a metal pipe filled with powder and set off by a lighted fuse. The type of bomb used in the bombing of the Park police station was not determined immediately. A special U.S. Army bomb squad was summoned to the scene from the Presidio nearby. After the bombing, all district police stations in San Francisco were ordered to secure all doors and exits and post a guard.

Would it be surprising the Zodiac Killer after reading and referencing the attack on Park Police Station, that he would then focus his bomb threats in close proximity to another police station on April 20th 1970 and June 26th 1970. The diagram of the bomb location on April 20th 1970, coupled with the radians and inches values from July 26th 1970, leaves little doubt that the unfortunate murder of Brian McDonnell was the catalyst for his remaining bomb threats towards Ingleside Police Station in 1970. It is also unsurprising that after reading headlines such as "Six Officers Injured in Blast Showering Big U-Shaped Staples", that the Zodiac Killer would follow up his April 20th communication with the Dragon card on April 28th 1970, writing on the front of the card "I hope you enjoy yourselves when I have my Blast". He would repeat this approach on the card inner, stating "If you don't want me to have this blast you must do two things".

The Dragon card is thought to depict the Miguel de Cervantes Saavedra characters of Don Quixote and Sancho Panza. This may have been a deliberate choice on behalf of the Zodiac Killer, as these characters were featured in statue form within Golden Gate Park, the location of Park Police Station. The two locations are about one mile from one another. Despite claiming he wasn't responsible for the Park Station bombing, he certainly wasn't averse to mocking the police at a time of immense grief. The Zodiac Killer, despite making many threats to murder by use of bomb, constantly made excuses for not doing so. On November 9th 1969 he claimed that the bomb was ready for "future use". On April 20th 1970, the problem was "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". On June 26th 1970 he promised to annihilate a full school bus, "but now school is out for the summer". It seemed for the Zodiac Killer the lingering threat was all that was required, pouring huge doubt on him having any serious intentions of following through on his bomb threats towards San Francisco. Knowing that the police had to take the threats seriously was satisfactory enough for a killer who thrived on instilling fear in the Bay Area community.

The Zodiac Killer mailed the Button letter on June 26th 1970 promising us that the "The Map coupled with this code will tell you where the bomb is set". Thirty days later, on July 26th 1970, he would give us the near-full answer to the 32-Symbol code, which only required the number 5 added to it (Radians and 5 inches along the radians). He also drew the dark, black circle around the circumference of a second set of crosshairs to provide the exact angle we had to travel away from Mount Diablo.  However, when he constructed the Button letter, he was of the opinion that he had provided us with enough information to solve the conundrum of where the bomb was set. This in itself was a massive clue when you consider the code had only three repeating characters. The introduction to the Button letter stated "I have become very upset with the people of San Fran Bay Area. They have not complied with my wishes for them to wear some nice Zodiac buttons. I promised to punish them by anilating a full School Buss. But now school is out for the summer, so I punished them in another way. I shot a man sitting in a parked car with a .38". It is clear that this introduction has nothing to do with the code, and in no way can be manufactured to explain the meaning behind the 29 unique characters contained with the 32-Symbol code. Therefore, the solution to the 32-Symbol code was expected of us (by Zodiac) using only what he added to the Phillips 66 map. This appears impossible - but it is not. 

Obviously, the following has only been worked out in hindsight of knowing the answer to the Mount Diablo code. This is why the Zodiac Killer gave us the two crosshairs with the answers in the Little List letter a month later - he knew that the clues he gave us on the Phillips 66 map were scarce to say the least. The Zodiac Killer gave us very little when he drew the crosshairs on the Phillips 66 map, yet he still expected us to use this to solve the 32-Symbol code. This should have been the biggest clue of them all. There is absolutely no way anybody can individually decode 29 unique characters in the 32-Symbol code by using what the Zodiac Killer drew on the map, but the crosshairs on the Mount Diablo map can be used to identify where particular words began on the 32-Symbol code, from which we can then start filling in the blanks - much like the Harden's identified the double symbols on the 408 cipher to identify "kill", therefore beginning the process of decoding. Once you get your foot in the door, eventually the whole cipher starts peeling open like an orange. This exact same process had to be adopted to unravel the 32-Symbol code using the crosshairs on the Phillips 66 map. The key was devilishly simple, but extremely unlikely to have been unearthed without the benefit of hindsight. 

To unearth the position of the bomb we have to travel a certain distance around the circumference of the circle of the crosshairs, set to Magnetic North (17 degrees in 1970). Then we had to travel a certain distance away from the summit of Mount Diablo (marked as position X by the Zodiac) from that degree point. The first thing we had to discover was his likely target area. The map was of San Francisco & Vicinity, with all the Zodiac Killer's previous letters and bomb threats focused towards San Francisco and the police. Therefore, the Zodiac Killer likely expected us to explore this avenue first. But before we do that, let's explore the limited characters contained by the crosshairs above.

To find the angle around the crosshairs we have to consider that any number of degrees could fall over San Francisco from its north to south border, with no way of determining this figure from the information supplied. So, we have to look for a way of measuring an angle around the circumference of the crosshairs where only one figure is possible for the answer. This lay in the radian, because only 4 radians and magnetic north could fall inside San Francisco (beginning from his arrow pointer, set to magnetic north and traveling around the clock face he provided). No other radian value could land inside San Francisco. We now have to focus on the diagram above. Radians would travel around the circumference of the crosshairs, so let us take a punt that the repeating C in the 32-Symbol code was representative of crosshairs/circumference, and therefore the radians that traveled around them. These would be the first two words inserted into the 32-Symbol code below. 

There are two other symbols or characters inside the crosshairs on the Phillips 66 map. The first one is the X symbol, deliberately accommodated by the Zodiac Killer by not fully completing the intersecting lines of his crosshairs. He could easily have just drawn normal crosshairs over Mount Diablo and everybody would have known this was his beginning point, yet he carefully left this area free to insert the letter X. This alphabetic letter can be found in the 32-Symbol code, so let us again assume that this is the starting point for another word. The only other character visible inside the crosshairs on the Phillips 66 map is the (in part) filled-in red triangle. We will take the same approach we did with the X symbol, and assume that the filled-in red triangle is represented on the 32-Symbol code by the filled-in black triangle (again beginning a word). The black triangle is often used to depict a mountain. We now have the C, X and black triangle in the 32-Symbol code, all of which should be the beginning of words.

Just like the degrees argument above, we know that by using miles as a measurement, any number of miles from Mount Diablo to San Francisco can fall within its eastern and western borders. Therefore, the answer cannot be in miles. But using the map code of 6.4 miles to the inch only one figure of inches can fall inside the land mass of San Francisco - and that figure is five. We also know that if the black triangle in the 32-Symbol code begins a word, then that word can only be 6 letters in length before the next word kicks in with the X character. Miles doesn't fit this criteria, but inches does. We now have effectively inserted three words into our 32-Symbol code (shown below).

We know that only 5 inches from Mount Diablo lands in San Francisco, so it's now easy to insert the figure 5 before inches. We cannot insert the word "five" because "radians five radians" doesn't read fluently. Once we have added the figure 5 before inches, it's easy to add "and" into the sentence to read "radians and 5 inches". Whether the reversed letter F represented 5 is impossible to tell. The rest of the solution is now pretty easy to guess. We are left with Radians and 5 inches _ _ _ _ _ _ _ _ radians. Once a line is drawn radiating away from Mount Diablo at 4 radians and magnetic north, we then have to travel 5 inches along the 4th radian value. This gives us the final two words of the 32-Symbol code of "along the".

We now have the full answer of Radians and 5 inches along the radians. If this reasoning had been used between June 26th 1970 and July 26th 1970 and given to the police prior to the arrival of the Little List letter, the suggested solution to the 32-Symbol code would probably have been accepted when the Zodiac Killer wrote "PS. The Mt. Diablo Code concerns Radians and # inches along the radians" at the foot of the July 26th letter. Unfortunately it wasn't.

The Zodiac Killer used exactly the same concept in his 13-Symbol code by highlighting three 8's by circling them (representative of Jesus Christ, resurrection, infinity and a new beginning). These again were found to begin each element of the solution "Fk, I'm crackproof", which when inserted into the code was infinite and circular in nature. The first 8 began FK, the second 8 began IM, and the third 8 began CRACKPROOF. The letters K and M were already present in the code as an aid. Just like the 32-Symbol code, the Zodiac Killer gave us the answer to the 13-Symbol code on October 5th 1970, seemingly frustrated, or had become aware that his clues were too difficult and scarce in nature. In both the 13-Symbol and 32-Symbol codes, the Zodiac Killer created anchor points where each word was to begin. Once the month of October 1970 had rolled on by, the Zodiac Killer would never elaborate on the workings of his ciphers ever again.

The Mount Diablo Map and Code Solution    The Codes of Zodiac Never Required an External Solve

In a previous article entitled The Dick Tracy 340 Cipher we explored the idea that the "13 punch-holes" and "red crucifix decoder" of the October 5th 1970 communication, may have been giving us a clue into the "Paradice and Slaves" formation within the 340 cipher. While this may remain the case, there could be a more direct link between the 13-Hole postcard and the April 20th 1970 13-Symbol cipher (and a case of dual functionality). There is the obvious link of 13 characters in the April 20th 1970 code and the 13 punched holes, but there is also the common link of phraseology in "What is the price tag now" and "I am mildly cerous as to how much money you have on my head now". These were the only two times the Zodiac Killer asked about the bounty on his capture. There is also a link between both configurations. The 13-Symbol cipher had three circled number 8's positioned in the center of the code (with 4 characters either side and two between them). The 13-Hole postcard had three distinct punch-holes in the center of the formation (with 4 punch-holes either side and two between them).

When you look at the 13-Hole postcard it is clear that the Zodiac Killer had plenty of room to configure the punch-holes into any arrangement he liked, yet he chose to overload one line with ten holes, with just three on the other. One could be forgiven for believing there was purpose in this design. 

The April 20th 1970 and October 5th 1970 communications were littered with Christian symbolism. We have the Red Crucifix, the three 8's (which in Christian numerology represents Jesus, or Christ the Redeemer), the Celtic Cross and the Anchor (adopted by Christians as a symbol of hope in future existence). The number 8 (infinity) in Christianity is representative of eternal life, rebirth, regeneration or a new beginning. They all play into the belief of an afterlife. This brought forward the notion that the number 8 in the 13-Symbol cipher was the beginning of each element of the phrase "Fk, I'm crackproof" (as shown above in green). In the diagram above, one can see that the letter F becomes the 5th letter in both sequences, the letter I becomes the 7th letter in both sequences, and the letter C becomes the 9th letter in both sequences, with the K and M slotting in between. In short, the letters FIC in both instances are separated into three circles, positioned identically in both sequences. The use of circles in both the 13-Hole postcard and 13-Symbol cipher plays directly into the phrase "Fk I'm crackproof", which when placed around the already existing K and M in the code, forms an eternal and circular repeating sequence. The April 20th 1970 communication now satisfied the October 22nd 1969 challenge by cryptographer D.C.B. Marsh in the San Francisco Examiner, for the Zodiac Killer to reveal his name. The letter now read "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is Fk, I'm crackproof".                

The first three San Francisco Police officers killed in the line of duty in 1970 were Eric Zelms, murdered when he lost control of his firearm when investigating a pawn shop robbery on January 1st. The second was Brian McDonnell on February 16th 1970, who suffered devastating and sadly fatal injuries seven weeks later, when a bomb packed with fence staples exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. The third was Richard Radetich on June 19th 1970 at 5:25 am, who 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. He was sat in his police car near 643 Waller Street, San Francisco in the Lower Haight District.

The Zodiac Killer didn't personally name any of them, but referred to them indirectly when he stated "two cops pulled a goof", "I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station" and "I shot a man sitting in a parked car with a .38". Additonally, all three communications carried the message of his bomb-making. 

The April 20th 1970 communication not only threatened that there was "more glory in killing a cop", but provided us with imagery that showed he had already set aside a location for his school bus bomb. The Zodiac Killer had specifically chosen a bus route traveling from north to south with a steep embankment on the right and the sun rising to the east. When deciding where to place his bus bomb, one would think the killer would be drawing from experience with regards to the best location. The diagram of the bus bomb location in the April 20th 1970 letter would eventually be discovered to be the embankment directly opposite Ingleside Police Station and alongside the parking lot of the City College of San Francisco. The addition of two crosshairs on the July 26th 1970 "Little List" letter would expand on the Button letter (a month earlier), and show to a 98% accuracy that the target was the Southern Freeway embankment opposite Ingleside Police Station - which was also a bus route. This would effectively kill two birds with one stone for the Zodiac Killer. Was the Zodiac Killer familiar with the City College of San Francisco, having worked at this location or even studied there?   

The Zodiac Killer certainly wanted to paint a picture he was familiar with law enforcement practices, giving rise to the notion he may have worked at, or attended the City College of San Francisco, where he could possibly have crossed paths with Richard Radetich, who attended a criminology course prior to becoming a police officer with the San Francisco Police Department. Greg Corrales was a legendary San Francisco Police officer who knew Richard Radetich and stated that "Richard, who had recently been assigned to Traffic, regularly stopped at Ingleside Police Station to say hello to his former colleagues. He glowed when he talked about his new baby girl and his wife. He was an outstanding police officer and a devoted family man". It is clear that Richard Radetich took criminology classes at the City College of San Francisco before being assigned to duties at Ingleside Police Station just 850 feet east of the college. Richard Radetich had formerly been a student at Balboa High School, 585 meters to the east of Ingleside Police Station. This aligns Sgt. Richard Radetich at the City College of San Francisco (and likely parking lot) studying criminology, with the bus bomb designated for the eastern edge of the parking lot on an embankment, alongside a bus route traveling north to south (with the sun rising to the east), only 274 feet from Ingleside Police Station (where Radetich had worked) - and subsequently - the Mount Diablo code pinpointing this location. The Mount Diablo code letter would also indirectly reference the murder of Sgt. Richard Radetich on June 19th 1970.

It is highly unlikely that the Zodiac Killer was responsible for the murder of Sgt. Richard Radetich, with the previous observations just a simple case of unfortunate coincidences, but it still leaves pause for thought when you consider the location of the bomb had been earmarked in a letter two months in advance of his murder, on April 20th 1970. A letter that highlighted the bombing of Park Police Station and the murder of Brian McDonnell, with the claim that "It just wouldn't doo to move in on someone else's teritory". So, did the Zodiac Killer move to a territory slightly south of Park Police Station, the clue to which lay in the attached bus bomb diagram?

On February 16th 1970, a militant group placed a bomb packed with fence staples on the window ledge of the San Francisco Police Department Park Station, killing Sergeant Brian McDonnell and severely injuring and wounding nine other police officers. The Zodiac Killer had nothing to do with the brazen attack, but spurred on from his previous threats upon random police targets, managed to reference the Park Station bombing, in accompaniment to the diagram of a school bus on the Southern Freeway. The Zodiac Killer stated in the April 20th 1970 letter, that  "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". This killer had targeted six kids like sitting ducks and blindsided his seventh victim, because he was a coward. The idea that this man would target somebody who could shoot back was extremely unlikely, with the threat to escalate his attacks, more a case of creating fear and panic in the community, rather than his willingness to do so.

It was likely the newspaper coverage of the Park Station bombing that inspired his following two communications. The Dragon card mailed 8 days later, carried the introduction of "If you dont want me to have this blast you must do two things. Tell everyone about the bus bomb with all the details. 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 bombing at Park Station was believed early on to be the work of the Weather Underground or the Black Liberation Army, hence the Zodiac Killer's need to get some recognition by the requesting the wearing of Zodiac buttons and referencing Black Power. It may also be significant that he placed "I hope you enjoy yourselves when I have my Blast" right alongside a picture of Don Quixote and Sancho Panza, suggestive of a location. A statue of Miguel de Cervantes, Don Quixote and Sancho Panza can be found in Golden Gate Park in San Francisco, approximately one mile from Park Station (1899 Waller Street), which also sits in Golden Gate Park, in the southeast corner. This threat of a blast, in accompaniment to the imagery, indicative of a compassionless killer piggybacking upon the Park Station bombing, by suggesting a threat in the near vicinity. An ominous foreboding that was already embedded in the April 20th 1970 letter in the form of the school bus bomb diagram. Just two months later, on June 26th 1970, the Zodiac Killer would expand on his bus bomb diagram by supplying us with extra details. 

The Zodiac Killer had given us the drawing of his intended bomb location, complete with photoelectric cells, car battery and timer. But now was the time to "clue us in" on where it was buried (or where it was threatened to be buried). The location he had designated was just three miles south of the Park Station, right alongside Ingleside Police Station on the Southern Freeway. The Zodiac Killer's threat never materialized, but somebody else did move in on his promised territory, when on August 29th 1971, Sergeant John Young was shot and killed inside the Ingleside Police Station. Two men brazenly entered the reception area and thrust a 12-guage shotgun through an opening in the bullet proof glass, striking and killing Sergeant John Young and injuring a civilian employee.

A bomb placed on the embankment of the Southern Freeway (274 feet from Ingleside Police Station) is notable for another reason. The Zodiac Killer didn't state he would "annihilate a school bus" on June 26th 1970, he promised to "annihilate a full school bus", suggesting that the school bus would have to be near the terminus of its route. The Thomas More Catholic School had a bus route along the Southern Freeway, just yards from Ingleside Police Station, passing a location mimicking the bus bomb diagram (shown below in red), with the school itself situated in the southwest corner of San Francisco. Children traveling from all over San Francisco would have been seated on this bus as it drove south in the morning light. The sun would have been to the east, with the school bus exiting the freeway extremely close to the school. It most certainly would have been full as it passed the proposed bomb location.

The Zodiac Killer threatened to kill police and place bombs, but he will be ultimately remembered for targeting the young and defenceless - and just like most serial killers - be recognized for the coward he was.  

The problem with solving the Zodiac Killer's 32 Symbol cipher and Phillips 66 Map code, is a failure to follow the instructions given by the killer in the June 26th 1970 letter and its follow up on July 26th 1970. The Zodiac Killer stated "The map coupled with this code will tell you where the bomb is set.  You have untill next Fall to dig it up". This tells us that the solution to the 32 symbol cipher will not supply us with the exact position of the supposed bomb. Any solution to this 32 character code pinpointing the exact position of the bomb will be incorrect, because this can only be realized by coupling it with the map. Therefore, the position of the bomb to be set, was a combination of both code and map.

In his following letter he stated "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". This tells you that the code is about radians and inches but not necessarily the entire solution. Any solution to the position of the bomb that doesn't use radians and inches (as implicitly stated by the killer) will be wrong. The phrase "P.S. The Mt. Diablo code concerns Radians + # inches along the radians" would supply the inches value, hence the hashtag before inches, along with the arrow beneath, instructing us to insert a value here. This isn't rocket science - the hashtag is widely recognized as a number sign, so by placing this immediately before the word "inches", the Zodiac Killer is telling us to insert a number before inches. The only way to find a bomb in Northern California using his instructions, is to travel a set amount of radians around his crosshairs, and then subtend a set amount of inches from it. In this case, a number of radians around Mount Diablo and a number of inches from it. Placing a hashtag and arrow before the word "inches", is rather a giveaway that a number value should precede it. Even the map code was 6.4 miles to the inch. Any solution that gives us the answer in degrees or miles is wrong, because "The Mt. Diablo code concerns Radians + # inches along the radians". We need to follow his instructions. This is why any theory of crime scene locations being chosen because they are separated by a radian or near radian value, is wrong also. The whole premise of the June 26th 1970 letter was to discover the location of his bomb, not measure angles between crime scenes or any other object we choose to construct or imagine

The Zodiac Killer gave us crosshairs superimposed over Mount Diablo with an arrow pointer set in the north facing position, "to be set to Mag. N". He allocated it a zero position, with a 3, 6 and 9 in the form of a clock face around its circumference. This was to instruct us to travel clockwise around the circumference of the crosshairs, to be set at 17 degrees (which was the magnetic north value in 1970). We had to travel a set amount of radians around his crosshairs over Mount Diablo, in addition to this value of 17 degrees. So, we are looking for a set amount of inches and a set amount of radians. The Zodiac Killer was incapable of keeping secrets and resisting putting pen to paper, so just one month later he gave us the answer, when the July 26th 1970 letter arrived at the San Francisco Chronicle.          

Never done before or since by the Zodiac Killer, he drew a big fat zero around the circumference of his crosshairs with SFPD alongside it. This represented the San Francisco Police Department. This bold, black circle sat at 246.2 degrees, which is 4 radians and magnetic north. This was the radian component of "The Mt. Diablo code concerns Radians + # inches along the radians". The answer was 4 radians. All we had to do now was find the "inches" value.

The Zodiac Killer mailed virtually every correspondence to the San Francisco Chronicle, describing the makeup of his bomb on November 9th 1969. He followed this up with a diagram of a school bus and photoelectric cells on April 20th 1970, referencing 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 of San Francisco. The Zodiac wrote about the "blast" he was going to have when he mailed the Dragon card on April 28th 1970. All of these communications directed towards the San Francisco Chronicle indicating he was constructing a bomb, with the SFPD attribution totaling zero adorning many. Therefore, it's pretty obvious that placing SFPD around the circumference of his crosshairs, next to a big fat zero and set to a value of 4 radians and magnetic north (4 X 57.3 + 17), indicates that the target for the bomb is San Francisco - or more specifically - the San Francisco Police Department. When the above crosshairs are set over Mount Diablo, we now have to travel 4 radians and magnetic north from the peak of the mountain. Let us now find the inches value to be inserted into "Radians and # inches along the radians".

We actually don't have to look hard to find the answer. The land mass and geography of San Francisco is such, that only 5 inches can fall over it. Using the map scale of 6.4 miles to the inch, anything less than 5 inches, and anything more than 5 inches, doesn't fall inside San Francisco. Therefore, there is only one answer. The same applies to the radians value. Anything more or less than 4 radians and magnetic north (such as 5 radians and magnetic north, or 3 radians and magnetic north), doesn't fall inside the geography of San Francisco. A bomb threat on San Francisco (hence SFPD=0), can only be 4 radians and magnetic north, and 5 inches along that radian value. The choice of words by the Zodiac Killer when he wrote "Radians and # inches along the radians". were chosen carefully. We were instructed to find "radians", and an amount of "inches" along the amount of "radians" we found. Once we found the radians value, we would travel 5 inches along that radian. The complete answer to where the bomb was to be set, was "4 Radians and 5 inches along the radian". But this wasn't the answer to the 32 symbol cipher, because the Zodiac Killer explicitly stated "The map coupled with this code will tell you where the bomb is set". Therefore, the simplest answer to the code should be Radians and 5 inches along the radians (consisting of 32 characters). This could be why he capitalized the first Radians and began it on a separate line. The answer to the map was the superimposed crosshairs of the bold, black circle sitting at 246 degrees (4 radians and magnetic north). The two "coupled" together gave us the full answer. However, Druzer, an avid Zodiac researcher, came up with a solution to the 32 character code which I believe is correct, when he suggested Estimate: four radians and five inches. This solution not only satisfies the 32 characters, but correlates three plaintext letters to the only three repeating ciphertext characters in the code, thereby providing a perfectly valid key. See The Blast Estimate of Zodiac and The Blast Estimate of Zodiac (Part Two).

The map scale is 6.4 miles to the inch. This gives us a distance of 6.4 multiplied by 5 (inches). Therefore, the bomb was to be set at 4 radians and magnetic north, and 32 miles from the peak of Mount Diablo. The only San Francisco Police Department that comes anywhere close is Ingleside Police Station. This San Francisco Police Department sits at 30.96 miles from the peak of Mount Diablo (4.84 inches). It also sits at 248 degrees from the peak of Mount Diablo (4.03 radians).

The Zodiac Killer gave us a rough guide of 4 radians and magnetic north, and 5 inches (hence the word "estimate"). If he had given us the exact measurement, it would have been 4.03 radians and 4.84 inches, He was clearly giving us an approximate measurement. Since Ingleside Police Station was the only San Francisco Police Department anywhere close to these measurements, it's fairly obvious this was his target. The Zodiac Killer's distance in miles was 96.8% accurate. His angular accuracy in degrees was 99.3%.   

The Zodiac Killer was targeting Ingleside Police Station for his bomb, but clearly he wasn't going to start digging a hole on the lawn of Ingleside Police Station. The Zodiac Killer also threatened to blow up a school bus on April 20th 1970, in which he drew us a diagram with a steep embankment on the right, with the sun rising to the east. This would suggest we should be looking for a bus route traveling from north to south (where the sun rises to the east in the morning), with a steep embankment to the right of the bus, where the Zodiac Killer can lay his photoelectric cells and conceal his bomb. He also has to access that roadway from a position of anonymity, with his vehicle parked at the top of the embankment in relative seclusion. What are the odds of that location being the exact closest portion of road to Ingleside Police Station, meeting all the criteria above. This would satisfy the drawing on the April 20th 1970 letter and the target of SFPD (Ingleside Police Station). The Zodiac Killer could metaphorically kill two birds with one stone.

So let us travel just 274 feet from Ingleside Police Station to the nearest section of road heading north to south.

Again, what are the chances that the area highlighted by the red rectangle would mimic exactly his bomb diagram of a school bus and embankment, as drawn in the April 20th 1970 letter. Not only that, but this would have been a school bus route in 1970. Children from the northern and eastern areas of San Francisco would use the school bus to reach St Thomas More Catholic School at 50 Thomas More Way. There is even a bus route road sign 38 feet from the proposed location of the bomb (whether it existed in 1970 I don't know). So, let us drop down to the exact position of the red rectangle and take a closer look.

All the Zodiac Killer had to do to access the embankment, was to access the parking lot of the City College of San Francisco and drive to its eastern edge - and at night - in relative anonymity to the police station, dig the bomb into the embankment. It is highly unlikely that the Zodiac Killer ever intended to plant a bomb, but this location fits all the criteria of targeting both a San Francisco Police Department and a school bus at the same time. It achieves his objective of targeting school children for maximum terror, and achieves his objective of "rubbing the pigs nozes in their booboos". The location of the bomb not only matches the diagram from April 20th 1970, but satisfies the criteria of the Mount Diablo map and code to an overall accuracy of 98%. The 32 character cipher is also answered. The Zodiac Killer had no intention of laying this bomb, but it was the threat that mattered most of all. The Zodiac Killer knew that the clues he provided us with on June 26th 1970 were inadequate in cracking the bomb location and code, so he gave us these additional clues in the Little List letter on July 26th 1970, one month later.

# Radian values are normally measured in a counter-clockwise direction, but the positioning of the bold, black circle at 246 degrees (4 radians and magnetic north), along with the north facing arrow pointer, the addition of the clock face set at zero, and the instructions to "set to Mag. N.", appears to indicate the Zodiac Killer measured his radians from the north position clockwise. In effect, he was multiplying the radian value of 57.3 by a factor of 4, set to magnetic north of 17 degrees (246.2).
Additional reading: The Anchor Points in the 32 and 13 Character Codes.    

Without any additional information the April 20th 1970 code is unsolvable. The Zodiac Killer was many things, but he wasn't a  half-witted imbecile with the brain of a gibbering lunatic when he designed this short 13 character code. In a newspaper article authored by Will Stevens on October 22nd 1969 in the San Francisco Examiner, Dr. D.C.B. Marsh challenged the Zodiac Killer no less than four times to supply us with his name in a cipher. Dr. Marsh stated in one section "The killer wouldn't dare...as he claimed in letters to the newspapers...to reveal his name in a cipher to established cryptogram experts". He added: "I invite Zodiac to send The American Cryptogram Association, care of Dr. D.C.B. Marsh, a cipher code - however complicated - which will truly and honestly include his name", quoting Edgar Allan Poe "that any cipher devised by man can be solved by man". Therefore, it was no great surprise when Zodiac's April 20th 1970 letter landed on the desk of the San Francisco Chronicle with the contemptuous opening line of "By the way have you cracked the last cipher I sent you? My name is------".  He knew his last cipher had not been solved, yet in mocking fashion was replying to the claim "that any cipher devised by man can be solved by man". The phrase "by the way" is used to introduce a new subject to be considered or to give further information. The Zodiac was effectively saying to Dr. Marsh he was wrong, now try this new cipher for size.

The Zodiac Killer chose to include eight characters from the English alphabet in his cipher, with 26 to choose from. Bearing in mind the challenge by Dr. Marsh was for Zodiac to reveal his name in the cipher, what are the odds of "NAM" forming consecutively, along with seven of the eight letters chosen from the alphabet being present in the word "name", being unintentional? Thereby leaving only K surplus to requirements. Although not impossible that this was just coincidental, one could argue that the N, A, M and E were chosen deliberately, considering the challenge by Dr. Marsh and the mocking introduction to the cipher by the Zodiac Killer. Did the Bay Area murderer, responding to the proposition of the eminent cryptographic expert to supply his "true identity" and "name", include his "identity" on line 20 of the 340 cipher, and use the word "name" in the Z13 just five months later?

Was the Zodiac Killer was just playing games with The American Cryptogram Association, determined not to have a further two ciphers cracked in a matter of days? - and thereby avoiding the acute embarrassment of creating "a cipher designed by man that can be solved by man". After the challenge on October 22nd 1969, the Zodiac Killer was going to design the remaining ciphers on his terms, to which he would ultimately reveal the answers. He wasn't going to allow Dr. Marsh the satisfaction of using cryptographic techniques to pry open his ciphers, so used the wording of Dr. Marsh "to send a cipher code, however complicated" against him, by sending two of the most infantile ciphers possible.

If we strike out the seven letters that have now formed "NAME" we are left with "NAME K". If this was the beginning letter of his surname, then the first circled 8 could represent his forename. So, if we are looking for an expanded declaration of his name using both forename and surname in later communications, we would be looking for a two letter combination, ending in K. But in addition, this would have to be accompanied by some pertinent text alongside the two letter declaration. This occurs in only one subsequent communication of the Zodiac Killer.   

You will notice how he begins this section of text, with "There are reports city police pig cops are closeing in on me". The text refers to the notion that law enforcement could possibly be close to capturing him, with the last word of "me" followed by a comma. One would therefore expect the next line to be a reaction by him in relation to this news. This has long been thought to be the abbreviated word "fuck" - an approach he didn't take in the August 4th 1969 Debut of Zodiac letter, when he wrote "When I hung the phone up, the damn X@ thing began to ring & that drew his attention to me + my car". The two letters of Fk may very well have been his initials - and a declaration that he "Fk, was crackproof". It may also be the answer to the 13 Symbol cipher, when responding to the challenge of Dr. Marsh.

If "Fk, I'm crackproof" was the answer to the 13 Symbol cipher, then one would have expected the Zodiac Killer to have designed the cipher with some markers present, that the answer could be fitted around later. Especially if no cryptographic technique was required. The phrase of "Fk, I'm crackproof" was the perfect response to Dr. Marsh, in that Zodiac could satisfy the request of Dr. Marsh by giving us his name, albeit in the shortened format. He began the April 20th 1970 letter by stating "By the way have you cracked the last cipher I sent you? My name is------". He responded immediately with his name (FK), before rubbing Dr. Marsh's "noze in his booboos" by declaring he was crackproof, having also just taunted the cryptographic expert with the mocking introduction of "have you cracked the last cipher I sent you?". The Zodiac Killer knew that Dr. Marsh would never solve his Z340 and Z13 ciphers when he designed them, because they couldn't be solved using standard cryptographic methods - and more importantly - the answers were 6 months in the making.

The circled eights (The number 8 in the Bible represents a new beginning) seemed to have extra significance compared to the other characters in the cipher. Because the Celtic Cross and Anchor have relevance in Christianity, it was considered that the number 8 was the beginning of each word. The three circled eights, along with the K and M inside them, were the markers I described earlier, so that his later solution would be understood. All we had to do now, was place the phrase "Fk I'm crackproof" into the 13 Symbol cipher, with each number 8 beginning each element of the phrase.

The completed introduction to the April 20th 1970 letter now read perfectly with respect to the Zodiac Killer giving us his name: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof". And so did the phrase "There are reports city police pig cops are closeing in on me, Fk I'm crackproof". Placing his real name in the 13 Symbol cipher was never a realistic proposition - and even if this had been done - it would never have been revealed and could never be proven. The only way a solution to the 13 Symbol cipher could be proven beyond any doubt, was for the Zodiac Killer to give us the answer. He obliged on October 5th 1970, as he did for the Z32 on July 26th 1970 and the Z340 on October 27th 1970. Proving this is the answer to the Z13 in isolation, is nigh on impossible, but when all three ciphers can be answered in three consecutive communications using only the words of Zodiac, it exposes a killer unable to resist temptation. The Zodiac Killer simply didn't have the temperament to take his secrets to the grave. 

In a previous article, The Secret Codes of Zodiac, we explored the idea that cryptographer D.C.B. Marsh dropped the name Edgar Allan Poe into his San Francisco Examiner newspaper article on October 22nd 1969, hoping that Zodiac would take the bait and design a cipher using techniques employed or featured by Edgar Allan Poe in one of his essays. We showed how the 13 character cipher of April 20th 1970 resembled a cipher technique shown in A Few Words On Secret Writing. The alphabet in both instances seemed split into two halves, with the 13 character Zodiac cipher beginning with A and ending with M. There was also a letter-writer who contacted Poe but "declined giving his name in full", dating the envelope April 21st 1841. Additionally, there was a Dick Tracy style technique mentioned in A Few Words On Secret Writing similar to that employed by Zodiac in his 340 cipher, 13 Hole postcard and Halloween card. But what if there was a cryptographic technique featured in A Few Words On Secret Writing that could directly produce the figure 888, clearly visible front and center of the Zodiac Killer's 13 character cipher. 

The Zodiac Killer had certainly made the figure eight the centerpiece of his coding on April 20th 1970, not only using three, but circling them as if to imply greater meaning. Was the circling of the number eights a hint towards the technique used in the coding? When we look at the first paragraph of A Few Words On Secret Writing, it features a technique using two wooden cylinders (scytala) as a method of coding, but directly underneath the example of coding in the essay, where the alphabet is split A to M, and N to Z, lies the important paragraph  It states;

A letter composed of such characters would have an intricate appearance unquestionably. If, still, however, it did not give full satisfaction, the idea of a perpetually shifting alphabet might be conceived, and thus effected. Let two circular pieces of pasteboard be prepared, one about half an inch in diameter less than the other. Let the centre of the smaller be placed upon the centre of the larger, and secured for a moment from slipping; while radii are drawn from the common centre to the circumference of the smaller circle, and thus extended to the circumference of the greater. Let there be twenty-six of these radii, forming on each pasteboard twenty-six spaces. In each of these spaces on the under circle write one of the letters of the alphabet, so that the whole alphabet be written — if at random so much the better. Do the same with the upper circle. Now run a pin through the common centre, and let the upper circle revolve, while the under one is held fast. Now stop the revolution of the upper circle, and, while both lie still, write the epistle required; using for a that letter in the smaller circle which tallies with a in the larger, for b that letter in the smaller circle which tallies with b in the larger &c. &c. In order that an epistle thus written may be read by the person for whom it is intended, it is only necessary that he should have in his possession circles constructed as those just described, and that he should know any two of the characters (one in the under and one in the upper circle) which were in juxta-position when his correspondent wrote the cipher. Upon this latter point he is informed by looking at the two initial letters of the document, which serve as a key. Thus, if he sees a m at the beginning, he concludes that, by turning his circles so as to put these characters in conjunction, he will arrive at the alphabet employed.

We know the Zodiac Killer often drew his inspiration from deep history, such as the short story The Most Dangerous Game by Richard Connell, first published on January 19th 1924, and The Mikado (1885), so what if he took this concept of two circles with a common center and looked for a cipher technique he could plagiarize in his April 20th 1970 letter. But more importantly, a technique of coding that had previously featured three eights (888) in its design.  

The Union Cipher Disk from the American Civil War was 3.75 inches (95 mm) in diameter and made of light yellow heavy card stock. It consisted of two concentric disks of unequal size revolving on a central pivot. The disks were divided along their outer edges into 30 equal compartments. The smaller inner disk contained letters, terminations and word pauses, while the outer disk contained groups of signal numbers. For easier recognition, the number eight represented two. The initials A.J.M. represent the Chief Signal Officer General Albert J. Myer.

A cipher disk is an enciphering and deciphering tool developed in 1470 by the Italian architect and author Leon Battista Alberti. He constructed a device, (eponymously called the Alberti cipher disk) consisting of two concentric circular plates mounted one on top of the other. The larger plate is called the "stationary" and the smaller one the "moveable" since the smaller one could move on top of the "stationary". The first incarnation of the disk had plates made of copper and featured the alphabet, in order, inscribed on the outer edge of each disk in cells split evenly along the circumference of the circle. This enabled the two alphabets to move relative to each other creating an easy to use key. Rather than using an impractical and complicated table indicating the encryption method, one could use the much simpler cipher disk. This made both encryption and decryption faster, simpler and less prone to error. Wikipedia.

The single and triple 8 number is featured heavily within the design of the Union Cipher Disk, with the 888 representing "tion".
Not only did the split alphabet of Edgar Allan Poe's 13 characters appear in the Zodiac code of April 20th 1970, along with the near date of April 21st, but the concentric circle cipher technique explicitly detailed in A Few Words On Secret Writing, can be found in the American history of the Union Cipher, with the number 8 front and center of everything, including the number 888.

On October 22nd 1969, the San Francisco Examiner and Dr. D.C.B. Marsh of The American Cryptogram Association designed a newspaper article with the express intention of trapping the narcissistic Zodiac Killer into inadvertently giving us his name, by carefully dropping key words into the framework of the article. The Zodiac Killer, it can be argued, took up the challenge and was led by the wording in the article. Dr. D.C.B. Marsh stated "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allan Poe, that any cipher created by man can be solved by man". 

It is perfectly conceivable that by dropping the name of Edgar Allan Poe, who was synonymous with coded challenges to his audience, into the newspaper article in an offhand way, Dr. D.C.B. Marsh was probably hoping the Zodiac Killer would use the techniques of Poe in offering us his name in subsequent ciphers. This would allow Marsh to narrow down the avenues of encryption used in any future Zodiac correspondence. When we consider the November 8th 1969 and April 20th 1970 codes of Zodiac, in comparison to Poe's A Few Words on Secret Writing, it is conceivable that the Zodiac Killer brought an essay from the last century into the heart of the Bay Area and presented this historic offering to The American Cryptogram Association.

So, after reading this newspaper article, the Zodiac Killer toddled off to the nearest library and searched for the works of Edgar Allan Poe. He arrived at A Few Words on Secret Writing - and remembering that Marsh had invited him to create a cipher "however complicated" - the Zodiac Killer took a prompt from the Poe essay and did completely the opposite. Wouldn't it be expected by observers, having had his 408 cipher cracked in a matter of days by the Harden's - and being challenged by Marsh to create a cipher "however complicated" - that the Zodiac Killer would dish out the mother of all ciphers. A cipher so devilishly fiendish, we would still be sweating over it 50 years later. The Zodiac Killer, knowing this would be expected of him, did completely the opposite and created a cipher on November 8th 1969 so unbelievably easy, that it still slipped through the cracks of the over-thinking mind. Not only that, but he got his idea from the wording of Edgar Allan Poe, as Marsh had hoped. 

The essay of Poe stated "Many of the cryptographs were dated in Philadelphia, and several of those which urged the subject of a bet were written by gentlemen of this city. Out of, perhaps, one hundred ciphers altogether received, there was only one which we did not immediately succeed in resolving. This one we demonstrated to be an imposition — that is to say, we fully proved it a jargon of random characters, having no meaning whatever". The Zodiac Killer wasn't one in a hundred, more like one in several million, so he certainly wasn't going to play by the rules. He now knew that he was going to create a cipher of nonsense, but not entirely without meaning.

The Zodiac Killer studiously continued down the essay just one paragraph, until the wording triggered off the second light bulb in his head. It stated "A very common, and somewhat too obvious mode of secret correspondence, is the following. A card is interspersed, at irregular intervals, with oblong spaces, about the length of ordinary words of three syllables in a bourgeois type. Another card is made exactly coinciding. One is in possession of each party. When a letter is to be written, the key-card is placed upon the paper, and words conveying the true meaning inscribed in the spaces. The card is then removed and the blanks filled up, so as to make out a signification different from the real one. When the person addressed receives the cipher, he has merely to apply to it his own card, when the superfluous words are concealed, and the significant ones alone appear. The chief objection to this cryptograph is the difficulty of so filling the blanks as not to give a forced appearance to the sentences. Differences, also, in the handwriting, between the words written in the spaces, and those inscribed upon removal of the card, will always be detected by a close observer".

Or, the card is punched with 13 holes, which when placed in true 'Dick Tracy' style over the 340 cipher, reveals the skeletonized version of Paradice and Slaves bisecting the cipher, 17 by 17 in cruciform. The rest of the 340 cipher filled with random noise, but fashioned in such a way to give the appearance of design, by forming the tell-tale signs of a real cipher. The Zodiac Killer even had the brazen cheek to correct one character of nothing, thereby feeding the false notion of a cipher he was conscientiously trying to get right. He even had the time to sign his work of art on the bottom line of his masterpiece. A work of art, but a work of fiction, that has been believed as credible for longer than Robert Graysmith. 

Several paragraphs later, and in order, the Zodiac Killer arrived at the Marsh trigger. Remember the challenge laid down by the eminent cryptographer: "Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name - in cipher code - would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code, which will truly and honestly include his name". This challenge is whirring around Zodiac's brain when he observes the piece of text in Poe's essay that mimics the challenge of Marsh. The text reads "This challenge has elicited but a single response, which is embraced in the following letter. The only quarrel we have with the epistle, is that its writer has declined giving us his name in full. We beg that he will take an early opportunity of doing this, and thus relieve us of the chance of that suspicion which was attached to the cryptography of the weekly journal above-mentioned — the suspicion of inditing ciphers to ourselves. The postmark of the letter is Stonington, Conn. S———————, CT., APRIL 21, 1841".

When we consider the challenge of Dr. D.C.B. Marsh to encourage the Zodiac Killer to give us his name in cipher form, with an encryption technique of a split alphabet presented in A Few Words on Secret Writing (shown below) - in combination with the postmark of April 21st above - then it is rather revealing that Zodiac should begin his April 20th 1970 cipher with "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. My name is....", and form it into 13 characters beginning with A, and ending with M. The Zodiac Killer was kind of mischievous like that.

It turned out that Zodiac didn't give us his name in full in the 13 character cipher, but he did give us something.