The Zodiac Killer gave us two working electrical circuits in his November 9th 1969 and April 20th 1970 bomb diagrams, threatening to blow up school buses in California. But how familiar was the Zodiac Killer when it came to circuitry and electronics? Did his profession require a knowledge of electronics, or did he simply copy the bomb-making designs from the publications he read?

​In the last article it was shown how the word "radians" began on the ciphertext symbol of Omega (in the Z32 code), taken from the concept that "The Mt. Diablo Code concerns Radians & # inches along the radians" formed the basis of the Z32 answer. When you consider that the Zodiac Killer placed a bold, black circle in his crosshairs with SFPD alongside (in his Little List letter), positioned at 4 radians and magnetic north, it becomes fairly obvious that the target was San Francisco. Only "four radians and five inches" fell inside San Francisco using the map scale provided.

If the Zodiac Killer was fairly adept in his knowledge of electrical circuits (having used the term radians), he would have known that "Radians and angular velocity are terms that are commonly used in AC theory and AC measurement. Most of the electric energy used commercially is generated as Alternating Current (AC). The main reason Alternating Current is used is that alternating voltage may be easily raised or lowered in value. This is a tremendous advantage in electrical distribution systems, allowing AC power to be generated and distributed at a high voltage and reduced to a more practical voltage at the load". Link to the Electronics Technician Training website. The Zodiac Killer would likely have known that "angular velocity" is represented by the lowercase Omega sign (ω), and that "angular velocity is another term that's related to Radian measure. Therefore, Omega is equal to so many radians per second. It is the time rate of change in angular displacement. This is equal to the distance traveled by the conductor, which is measured in radians, divided by the period (T), time taken for one revolution". So did the Zodiac Killer use the uppercase Omega sign as a subtle clue to "radians", bearing in mind the Z32 was comprised of uppercase letters?    

Therefore, if we go with the hunch that the "radians" word begins on the Omega part of the code (see above), how likely is it that "radians and five inches" would perfectly complete the Z32 code from character 13 to character 32. All we have to do then is add the word "four" before "radians" to complete characters 9 to 12, thereby creating "four radians and five inches" (from character 9 to character 32). Then we have to fill in the three repeating ciphertext characters with the plaintext characters of E, S and A. The answer of "estimate" is now fairly obvious, bearing in mind the target chosen by the Zodiac Killer was extremely unlikely to have fell on an exact amount of radians and inches. It could be argued that the Zodiac Killer gave us the three repeating ciphertext characters within the word "estimate", to give us a chance at uncovering the final part of the solution. The rest of the solution he had already given us in the phrase "The Mt. Diablo Code concerns Radians & # inches along the radians".."The Mt. Diablo Code concerns (FOUR) RADIANS & # (FIVE) INCHES along the radians".

Despite this concept being obvious once presented, the idea was undoubtedly a brilliant discovery by Zodiac researcher, Druzer, who unfortunately will never get the credit he deserves. This discovery, while incredibly easy to present, required somebody of the caliber of Druzer to unearth the answer. The simplicity of this solution is its strength, when compared to the fantastical and convoluted presentations you will encounter throughout the internet. Did the Zodiac Killer just read this information from the various publications that came his way, or did he have an intrinsic knowledge of electrical circuitry, so enabling him to create fully functioning bomb-making diagrams?           ​

In 2020, the Zodiac Killer's 32 character code was solved by Druzer, who put forth the answer of "Estimate Four Radians and Five Inches". The Zodiac Killer, knowing the code was unsolvable with only three repeating characters, pretty much gave us the answer on July 26th 1970, when he wrote "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". The "code concerns Radians & # inches" meant using "radians and inches" in the answer, with the hashtag key the obvious giveaway.

Once "four radians and five inches" was placed in the code from character 9 to 32, only the word "estimate" satisfied the three repeating ciphertext characters in the 1 to 8 position in the code. The four radians and magnetic north of 246.2 degrees (229.2 + 17 degrees), fell slightly shy of Ingleside Police Station (SFPD), which was the target highlighted by the black circle within the crosshairs. You may come across a disingenuous individual cloaking his identity under the pseudonym of VT Squire, who insists that I manipulated the overlays to achieve a preconceived and desired result. However, as you can see in the 2020 article linked above, the accuracy was never exact. Four radians and magnetic north measured 246.2 degrees, while Ingleside Police Station sat at 251 degrees. Manipulating the overlays to produce an exact result would completely negate the point of having "estimate" in the Z32 code. 

​The Zodiac Killer once again used radians in his Bus Bomb letter approximately 7 1/2 months earlier (November 9th 1969), when he threatened to target Salesian High School (likely with a bomb). The crosshairs he provided in this instance, highlighted the numbers 6, 8, 9, 10 and 11 on a clock face, which when tilted close to magnetic north in 1970 and centered over Mount Diablo, landed over the five attack sites he was claiming at Lake Herman Road & Blue Rock Springs (line 10), Lake Beryessa (line 11), Presidio Heights (line 8) and San Jose (line 6). See below. The Zodiac Killer falsely claimed the murders of Snoozy & Furlong in San Jose a day earlier in his Dripping Pen card. Only line 9 remained unanswered. Next to his crude crosshairs "clock face", shown here, he wrote "PS. Be Shure to print the part I marked out on page 3 or I shall do my thing". His "thing" seemed to be the targeting of schoolchildren, so it wasn't surprising that line 9 fell over the Salesian High School where Daniel Williams worked as a school teacher. Daniel Williams had received numerous threats from somebody identifying themself as the Zodiac Killer in the preceding weeks.

One has to remember when looking at the crosshairs on the Bus Bomb letter (and Little List letter), that these are crude designs not meant to be totally accurate. The 9 o' clock position is 270 degrees on a compass rose, therefore, 9 o' clock and magnetic north (of 17 degrees) is 287 degrees. One radian is approximately 57.3 degrees, so 5 radians is 286.5 degrees. Therefore, 5 radians equals line 9 tilted to magnetic north.

With the crosshairs "clock face" tilted close to magnetic north, line 9 falls over the Salesian High School.(9 o' clock position). Not only did somebody identifying as the Zodiac Killer target Daniel Williams with arsenic on November 2nd 1969, but the school where he worked was also targeted on November 9th 1969 by the Zodiac Killer, using a measurement of 5 radians. That's because the Zodiac Killer was responsible for both. The Zodiac Killer did exactly the same thing on June 26th 1970 (Button letter), when he used 4 radians to target the San Francisco Police Department (SFPD) with a bomb. On both the Phillips 66 map (mailed with the Button letter) and the Bus Bomb letter, the Zodiac Killer utilized the numbers on a clock face. In both instances, the 9 o' clock position has to be rotated clockwise by magnetic north to identify the target.

USING MOUNT DIABLO ON NOVEMBER 9TH 1969

On April 20th 1970, the Zodiac Killer referenced the Park Police Station bombing in San Francisco and the resulting death of Brian McDonnell on February 16th 1970. Eight days later, he mailed the Dragon card to the San Francisco Chronicle asking them to publish the workings of his bus bomb with all the details, with failure to do so resulting in him having his blast. The Zodiac Killer informed the San Francisco Chronicle that he would like to see some nice Zodiac buttons around town. On June 26th 1970, the Zodiac Killer had become upset because the people of San Francisco had not complied with his wishes to wear some nice Zodiac buttons, but had to delay his bombing of a school bus until the Fall, as school was out for the summer. However, he supplied us with a map of San Francisco & Vicinity, stating  "the map coupled with the code will tell you where the bomb is set". So, it's a real head-scratcher where the bomb was to be set? Was it San Francisco by any chance? Or was Fayçal Ziraoui correct when he identified a school in South Lake Tahoe, that wasn't even present on the Phillips 66 Map that Zodiac provided? Many have asked whether it is possible to find the location of the bomb without the extra clues he provided in the Little List letter on July 26th 1970 of "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". Clearly the Zodiac Killer thought it was, when he mailed the map and code on June 26th 1970.

From the above sarcasm, it is reasonable to conclude that the target was a school bus in San Francisco. So how do we find that location? The crosshairs he placed on the map where "0 was to be set to Mag.N", along with the clock face numerals, are a good indication that we must travel around the circumference of Mount Diablo and measure a certain distance from it. However, we can't use individual degrees as a measurement tool, because any number of degrees can fall over the land mass of San Francisco from north to south (and there isn't enough information on the map to conclude which number of degrees is correct). Therefore, we have to find an angular measurement where only one answer exists. If somebody had looked up radians in 1970, they would have concluded that only the whole measurement of 4 radians and magnetic north can fall inside the land mass of San Francisco between its northernmost and southernmost tips. No other radian value can fall within San Francisco. This would have to be the starting point. 

The map scale was in inches and miles, however, the answer could not be in miles because any number of miles can fall inside the land mass of San Francisco between its easternmost and westernmost tips. But using the map scale of 6.4 miles to the inch, only the whole measurment of 5 inches can possibly fall inside the land mass of San Francisco. Had somebody concluded the measurements in radians and inches immediately after receiving the Phillips 66 Map in 1970 using the scant information provided by the Zodiac Killer, then one month later when the Little List letter arrived stating "PS. The Mt. Diablo Code concerns Radians & # inches along the radians", they would likely have been taken seriously. The lack of information on the map meant that we had to be looking for measurements where only one answer was possible for the angle and distance. That answer was whole numbers of radians and inches over San Francisco. Since the code concerned radians and inches, it could be concluded that placing "four radians and five inches" in the code was the obvious choice, before finding the meaning behind the remaining eight characters that painted the full picture. The location the Zodiac Killer selected to claim his bomb placement was a function of roadside, school bus and San Francisco Police Department - so was very unlikely to satisfy such an exact measurement. 

The Zodiac Killer appeared to be using Mount Diablo as a reference point as early as November 9th 1969, when he mailed the Bus Bomb letter and supplied us with some crosshairs and five X's on its circumference. Using this diagram it is possible to determine that the Zodiac Killer was identifying Mount Diablo as his initial or center point. Mount Diablo was used for the purpose of land boundaries in the majority of Northern California and Nevada, with the summit used as the "initial point", the north/south meridian and the east/west baseline intersection point. However, because of the vastness of California, surveying required three "initial points" of Mount Diablo, Mount Pierce and the San Bernardino Mountain to form grid lines. The Zodiac Killer knew the prominence of Mount Diablo from an elevation standpoint, but very likely knew some of the history from a navigational perspective  - and why he chose this mountain as his "initial point".

In the Dripping Pen card the Zodiac Killer was claiming the brutal stabbings of Kathie Reyne Snoozy & Debra Gaye Furlong on August 3rd 1969. On November 12th 1969, somebody featured in the San Francisco Chronicle used the San Jose double murder in their analysis of the Bus Bomb letter crosshairs, very likely concluding the "initial point" was Mount Diablo, without actually referring to the mountain by name. When you look at the five X's around the circumference, it's fairly obvious that they all sit on the left side of the crosshairs center (from 180 degrees to 330 degrees). They were positioned at 6, 8, 9, 10 and 11 on a clock face. Therefore, the "initial point" must be to the east of all the confirmed attack sites. When we attempt to line up the uppermost X with the Zodiac Killer's uppermost crime at Lake Berryessa, it becomes quickly apparent that only one position satisfies four of the X's on the circumference, and that one X represents both Lake Herman Road and Blue Rock Springs. If we draw a line through the Lake Herman Road and Blue Rock Springs attack sites, the line passes directly over the summit of Mount Diablo and beyond. By moving the crosshairs "initial point" along this line, we can see that only one position satisfies at least four of the X's.     

The Zodiac Killer only gave us a rough drawing of his crosshairs, so any interpretation must take this into account. The above diagram, centered over Mount Diablo, lines up the five locations the Zodiac Killer was claiming as his murders (Lake Herman Road, Blue Rock Springs, Lake Berryessa, San Francisco and San Jose). The (unaccounted for) red line above, travels directly over the Salesian High School of Daniel Williams, who Zodiac targeted from October 23rd 1969 to November 5th 1969 by prowling his house, poisoning his drink, making malicious phone calls, and threatening to shoot him via the Martinez Police Department. His subtle threats continued in the Dripping Pen card and Bus Bomb letter, explained thoroughly in the article The Quest For Number Eight. This is why he wrote "PS. Be Shure to print the part I marked out on page 3 or I shall do my thing" next to the crosshairs on the Bus Bomb letter. That "thing" was a threatened attack on Salesian High School, depicted by the red line on the map. The orange line shows Magnetic North of 16.5 to 17.0 degrees in 1969. The tilted crosshairs are slightly shy of this mark. But remember, the Zodiac Killer only drew us a rough guide in his correspondence. These Bus Bomb crosshairs were the precursor to the Mount Diablo map on June 26th 1970, when the Zodiac Killer again used the mountain's "initial point" as a directional tool, but this time to locate a proposed bus bomb on the Southern Freeway by Ingleside Police Station, using four radians and five inches. The Mount Diablo Map and Code Solution.     

This is the image supplied to us by the Zodiac Killer on the Phillips 66 Mount Diablo map on June 26th 1970. By placing the numbers 0, 3, 6 and 9 around the crosshairs, akin to a clock face, and instructing us that 0 is to be set to Mag. N, the Zodiac Killer is telling us that we have to travel a certain amount of degrees around the clock face from point zero (set to magnetic north, which was 17 degrees in 1970).

The Zodiac Killer realized that the information he provided in the Button letter was insufficient to discover where he was planning to set the bomb. He also realized it was insufficient to solve the 32-Symbol cipher. That is why he placed two crosshairs in his next communication on July 26th 1970. One of the crosshairs contained the radians value, while the other crosshairs contained the inches value. Zodiac wrote:

"P.S. The Mt. Diablo code concerns Radians + # inches along the radians".

It was that simple - all we had to do was place the first crosshairs (shown on the right) over a compass rose. The center of the little black circle with SFPD next to it, landed extremely close to 246 degrees, which is 4 radians and magnetic north. That is the answer to the radians value. The target was SFPD.

The second crosshairs had the phrase "P.S. The Mt. Diablo code concerns Radians + # inches along the radians" written over it. Why would the Zodiac Killer place an arrow pointing before the inches value, if he didn't intend for us to place a number here? The answer could only ever be 5 inches, because using the Phillips 66 map scale of 6.4 miles to the inch, only 5 inches falls over San Francisco (4 & 6 inches falls into the sea).
​
The target of SFPD was therefore 4 radians and five inches from Mount Diablo. The target (to a 97.5% accuracy) was the Southern Freeway by Ingleside Police Station, explained in greater detail here.

Druzer and I have recently been working on the Mount Diablo map code solution, using the measurements of four radians and five inches supplied by the Little List letter crosshairs. Druzer came up with a solution to the 32-Symbol cipher that satisfied the three repeating ciphertext characters in the code, giving us an estimate of where the Zodiac Killer was threatening to "set his bomb". The target was the Southern Freeway alongside Ingleside Police Station, stated in a previous article as 4.08 radians (4 radians} and 4.84 inches (5 inches) from Mount Diablo, indicating that the Zodiac Killer was rounding off his values and giving us an estimate.

It has been stated on this site and elsewhere, that the 32 character code is unsolvable using conventional cipher techniques without the killer supplying us with a key. There are 29 unique characters within the code, making any solution practically unprovable. The solutions offered by using the 408 and 340 keys have produced less than convincing results, particularly when we consider that this code contains an "anchor" and "omega" symbol, not used in the 408 and 340 ciphers. Attempting to correlate the letters used in the code to written text in both the Button letter (June 26th 1970) and Little List letter (July 26th 1970) also produces negative results. Therefore, it could be argued, that a code containing 29 unique characters must have an alternative meaning, in accompaniment to the code solution of "estimate:four radians and five inches".

The Zodiac Killer gave us an estimate of 4 radians, but the actual figure (shown above) was 4.084 radians. That is, 4.084 multiplied by one radian value (57.3 degrees) to equal 234 degrees. When we add in the magnetic north which Zodiac instructed us to do (17 degrees in 1970), we get 251 degrees and the location of Ingleside Police Station. Could the 32 character code contain the value of 234 degrees, which once set to magnetic north, now identified the exact location of Ingleside Police Station? If we resort to basic numerology where A=1, B=2, C=3 etc, and add up the values of the alphabetical characters in the Zodiac Killer's 32 character code, we arrive at a total of 234 (or 234 degrees). When set to magnetic north, it gives us the value of 251 degrees, which when subtended from the peak of Mount Diablo passes directly over Ingleside Police Station and the Southern Freeway. "The map (set to 17 degrees magnetic north) coupled with the code of 234 will tell you where the bomb is set".

On July 26th 1970, the Zodiac Killer mailed the Little List letter with the important clues to the Mount Diablo mystery, stating "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". The answer would be about radians and inches. With the northern section of the map crosshairs positioned at zero and to be set to magnetic north, the Zodiac Killer gave us the approximate value of 4 radians and magnetic north (246 degrees) by the placement of the bold, black circle within the first crosshairs on the Little List letter (the Zodiac Killer's crude design was off by about 3 degrees).

The target was the San Francisco Police Department at Ingleside (SFPD). The second set of crosshairs on the Little List letter contained the hashtag (number sign) in the phrase above, with an arrow placed underneath, beckoning us to insert a number before inches. Only 4 radians and magnetic north, coupled with 5 inches could ever fall over San Francisco, constrained by its land mass. No other values can meet the requirement of targetting SFPD. To an overall accuracy of 98%, the location of the bomb was to be set on the embankment of the Southern Freeway just 274 feet from Ingleside Police Station. For the full story, read The Answer to the Mount Diablo Code.

My solution to the 32-Symbol code in the above article did not marry up the ciphertext to the plaintext adequately, however, Druzer, an invaluable contributor to both Zodiac Killer forums, supplied a solution that married up the three repeating ciphertext characters with corresponding plaintext characters. His solution took "PS. The Mt. Diablo Code concerns Radians & # inches along the radians". into "four radians and five inches" that satisfied the requirement of the Zodiac Killer's Mount Diablo code. This would ultimately provide us with 24 of the plaintext characters for the solution, leaving us 8 ciphertext characters to decode. Druzer came up with the answer, but how was this achieved?     

The problem that materialized, was where to place "four radians and five inches" within the 32-Symbol array. We needed an entry point. The clue had to exist within the ciphertext characters themselves. Two of the most notable ciphertext characters were the Anchor and Omega symbols (the latter of which had never been used before), so possibly it was this symbol that held the key of where to insert "four radians and five inches".

The Omega symbol can be written two ways (shown on the left), with a quick search on Wikipedia revealing information on the radian per second. The radian per second (symbol: rad⋅s−1 or rad/s) is the SI unit of angular velocity, commonly denoted by the Greek letter ω (omega). The radian per second is also the SI unit of angular frequency. The radian per second is defined as the change in the orientation of an object, in radians, every second. 

Using this as the entry point in our ciphertext characters, the word "radians" was placed at the beginning of the Omega sign in the code, hoping that the 24 plaintext characters of "four radians and five inches" would travel to the end of the code. Inserting "four" before "radians", It fell into the code seamlessly (as shown below).

Now we can add in the three plaintext characters represented by O, C and ∆ to the three repeating ciphertext characters in the first section of the code, like so.

Ingleside Police Station is actually 4.08 radians (4 radians} and 4.84 inches (5 inches) from Mount Diablo, so the Zodiac Killer was rounding off his values and giving us an estimate. As can be seen in the above diagram, the word "estimate" fits perfectly into the first eight characters of the code, giving us the final answer to the 32-Symbol code of "estimate: four radians and five inches". The Zodiac Killer was informing us that the answer to the Mount Diablo code of "four radians and five inches" was just an estimate to the location of the bomb at Ingleside Police Station (SFPD). The Merriam-Webster dictionary defines "estimate" as a rough or approximate calculation, which is exactly what it is.

In respect to the Mount Diablo code, the Zodiac Killer gave us two clues to where his bomb was to be set, in the form of two crosshairs on July 26th 1970. The first crosshairs contained a bold, black circle positioned close to 4 radians and magnetic north around its circumference (the Zodiac Killer's crude design was off by about 3 degrees). Next to this circle, the Zodiac Killer placed SFPD=0, indicating the target was a San Francisco Police Department. The second crosshairs were overwritten with the wording "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". The hashtag (recognized as a number sign) was positioned above a pointing arrow, beckoning us to insert a number value before inches. The answer is five inches, because this is the only value that falls over San Francisco from Mount Diablo using the map scale of 6.4 miles to the inch. The bomb was to be set alongside Ingleside Police Station, on an embankment bordering the Southern Freeway. For further explanation in simplified form, please visit here, or for more extensive coverage read the article The Answer to the Mount Diablo Code.

Footnote: Ordinarily radians would be measured counter-clockwise, but 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 in this instance. Which is why it was no fluke that the bold, black circle fell exactly at 4 radians and magnetic north.

The Blast Estimate of Zodiac (Part Two)

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.

The Zodiac Killer often responded to the newspaper articles written about him, usually in close proximity to their release. The Dripping Pen card had likely been purchased subsequent to the morning of October 25th 1969 in response to the last San Francisco Chronicle article by Paul Avery. If the 340 character cipher had been specifically designed to compliment this card, then it too was crafted subsequent to October 25th 1969. As the title attributed to this communication suggests, this greeting card featured a dripping pen on its front face, accompanied by the wording "Sorry I haven't written, but I just washed my pen". The Avery article read "Zodiac struck last on October 11 when he gunned down cab-driver Paul Stine on Washington Street in Presidio Heights. He revealed himself the killer in a letter sent to the Chronicle three days later. Since then he has remained silent".

Bearing in mind the wording "since then he has remained silent", it could be argued that the chosen card of "Sorry I haven't written" was purposefully selected in response to this article - and therefore chosen by the Zodiac Killer after October 25th 1969. The paragraph in the newspaper article also referred to Washington Street, thereby completing the phrase on the card "but I just washed my pen". The last observation is probably a little far-fetched, and heavily reliant on the Zodiac Killer being able to find a greeting card apologizing for being silent, as well as containing a word related to Washington Street. Extremely unlikely, but not impossible.

Then, the day before the November 9th 1969 'Bus Bomb' letter, came the newspaper article detailing the attempted murder of Richmond school teacher, Daniel Williams. Somebody claiming to be the Zodiac Killer made sadistic phone calls spanning October 23rd 1969 and November 2nd 1969, and culminating in a soft drink in his refrigerator being laced with arsenic. This failed murder plot may have inspired the Zodiac Killer (if the poisoner) to insinuate his continued pursuit of Daniel Williams, by stating "I though you would nead a good laugh before you hear the bad news" and "up to the end of Oct I have killed 7 people". On November 12th 1969, the San Francisco Chronicle released information on the Dripping Pen card and Bus Bomb letter under the banner of I've Killed Seven, The Zodiac Claims.

This newspaper article featured the observations of an individual with respect to the X's on the Bus Bomb crosshairs (see right). This observation was suggested in the article The Promise of Murder on Line 5.

I believe the person who initially made this suggestion was almost certainly correct. However, when I floated this idea on November 23rd 2020, I was fully aware of the Mount Diablo map and crosshairs accompanying the Button letter, which was mailed to the San Francisco Chronicle on June 26th 1970. I positioned the Bus Bomb crosshairs over Mount Diablo and rotated them slightly clockwise, so that a line drawn from the peak of Mount Diablo through four of the five X's passed directly over Lake Berryessa, Vallejo (where two attacks occurred), San Francisco and San Jose.

When we consider that this person made the observation on November 12th 1969, seven-and-a-half months before the Mount Diablo map was mailed by the Zodiac Killer (on June 26th 1970), the interpretation by this individual is extremely intriguing.  

The five cross marks cannot directly pinpoint the five claimed attacks in Benicia, Vallejo, Lake Berryessa, Presidio Heights and San Jose by superimposing them over a map. If you arrange any two X's over Lake Herman Road and Blue Rock Springs, the other three X's will never fall over Lake Berryessa, Presidio Heights and San Jose. The only way it is possible, is by placing the crosshairs over Mount Diablo (rotated clockwise} and drawing lines through the X's on the circumference. But this still leaves the 9 o' clock line unaccounted for. This is where Daniel Williams, the Richmond school teacher comes in. The sadistic phone caller to Daniel Williams may have wanted to target schoolchildren at the Richmond school where he worked (Salesian High School falls over the line drawn through the 9 o' clock position}. This is covered in the article A Killer on Line Five.

The newspaper article stated "Zodiac's letter contained five cross marks which possibly refer to attacks. Comparing these markings against a map, one interpretation that can be drawn is that they pinpoint Lake Berryessa, Vallejo (where two attacks occurred}, San Francisco and San Jose". It was effectively saying that five cross marks could pinpoint four locations (identifying Vallejo as the location where two attacks occurred). Despite classifying Lake Herman Road as Vallejo, the tight grouping of the first two attacks on the map would allow the observer to reach the same conclusion as shown in the above map. After all, this person didn't say "Zodiac's letter contained five cross marks which possibly refer to five attacks".

The Zodiac Killer likely chose Mount Diablo because of its use when surveying land boundaries in Northern California, with the summit used as the "initial point". Was it possible that the person behind the interpretation on November 12th 1969 had correctly identified Mount Diablo as the "initial point" to center the crosshairs over, by using the same reasoning as Zodiac? The Zodiac Killer himself classified Lake Herman Road and Blue Rock Springs under the banner of Vallejo (evident on Bryan Hartnell's car door), so when he provided five cross marks to signify four general locations, he was deliberately leaving the 9 o' clock line as a puzzle to the location of his next attack. He employed exactly the same technique, when substituting the X around the crosshairs with a bold, black circle around the circumference of the crosshairs on July 26th 1970, again designed to pinpoint the location of his next attack. On this occasion, it would be a school bus traveling on the Southern Freeway by Ingleside Police Station, positioned at 4 radians and magnetic north.   

After watching the very educational and insightful presentation of Let's Crack Zodiac (Part Four) by Dave Oranchak for the National Cryptologic Museum, the section about the X's positioned around the Bus Bomb crosshairs sparked a fresh interest. Dave Oranchak is correct when he identifies the difficulty regarding scale when overlaying the crosshairs over a map. The Zodiac Killer overlayed his crosshairs over Mount Diablo as part of the Button letter on June 26th 1970, which he followed up with a further clue in the Little List letter on July 26th 1970. The Zodiac Killer explicitly stated that the crosshairs were to be set to Magnetic North (17 degrees in 1970). Therefore, it wasn't particularly surprising that the center of the black circle around the circumference of the first crosshairs on the Little List letter, fell exactly at 4 radians when set to Magnetic North, ultimately identifying Ingleside Police Station as the focus for the bomb.

Two overlays were used to great effect in the June 26th and July 26th communications. It is with little doubt that the Bus Bomb crosshairs were designed to pinpoint locations as well. However, as Dave Oranchak pointed out, the scaling of such an operation is likely to lead to inaccuracy. Therefore, we have to treat the crosshairs on the Bus Bomb letter as a guide. Only a day earlier, the Zodiac Killer had listed his murder count on the Dripping Pen card, mailed to the San Francisco Chronicle on November 8th 1969. He chronologically listed the murders he was claiming by use of months, writing "Des, July, Aug, Sept, Oct = 7".

We know the Zodiac Killer had murdered five victims at Lake Herman Road, Blue Rock Springs, Lake Berryessa and Presidio Heights, but he added in the murders of Kathy Snoozy and Deborah Furlong in San Jose on August 3rd 1969. To this point, the Zodiac Killer had listed his victims, but always left us dangling with the promise of more murders. Would it be all that unusual if the Zodiac Killer again pinpointed these seven victims the following day by use of X's around the circumference of his crosshairs, just like he pinpointed 4 radians and Magnetic North around the circumference of his crosshairs in the Little List letter on July 26th 1970 - with both crosshairs overlayed over Mount Diablo. But in true Zodiac style, the promise of another location in which he would soon murder. If this were the case, we would expect one X on the circumference of the Bus Bomb crosshairs to be unknown.              

To a reasonable degree of accuracy, line [1] falls over Lake Berryessa and the murder victim Cecelia Shepard. Line [2] passes directly over Lake Herman Road and Blue Rock Springs, accounting for David Faraday, Betty Lou Jensen and Darlene Ferrin. Line [3] passes over Presidio Heights and the murder of Paul Stine. Line [4] passes over San Jose and the murders of Kathy Snoozy & Deborah Furlong. These were the locations of his seven victims which he had claimed just a day earlier. One line remains unknown. This line passes over Walnut Creek (where Elaine Davis was abducted from on December 1st 1969, and eventually murdered), as well as Richmond and San Rafael. Had the Zodiac Killer deliberately created this X on the 9 o'clock position as a teaser to his next destination of murder? Next to the bottom right quadrant of his crosshairs on the Bus Bomb letter, he wrote "Be sure to print the part I marked out on page 3 or I shall do my thing". Considering this section of text was placed next to the crosshairs with the X's, was his "thing" going to occur somewhere in the vicinity of Walnut Creek, Richmond or San Rafael, along the unknown line? As far as we know, no murders can be connected to the Zodiac Killer over the next few months in these locations, making you wonder whether this was just another threat that didn't materialize. Or it was simply just a game he was playing.  

FOLLOW UP ARTICLE: A KILLER ON LINE FIVE  

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.

It is fairly obvious by now that the Zodiac Killer didn't just pluck Mount Diablo out of a hat for the starting point of his Mount Diablo code in the Button letter on June 26th 1970. He knew the history of Mount Diablo and knew that the peak of Mount Diablo was used for the purpose of land boundaries in the majority of Northern California and Nevada, with the summit used as the "initial point", the north/south meridian and east/west baseline intersection point. However, because of the vastness of California, surveying required three "initial points" of Mount Diablo, Mount Pierce and the San Bernardino Mountain to form grid lines.

The Zodiac Killer knew the prominence of Mount Diablo from an elevation standpoint, but very likely knew some of the history and purpose of Mount Diablo - and why he chose this mountain as his "initial point" for the code of radians and inches to be measured from.

It is true that only a tiny proportion of a population would understand what a radian is, but the conclusion drawn from the Zodiac Killer's use of radians as an angular measurement, that he must have been familiar with them through his profession or hobby, is not necessarily the case. He could easily have read a book, magazine, or newspaper article in the preceding hours, days, weeks or months to mailing the Button letter. While most people will not be knowledgeable to the concept of radians, it takes very little time to familiarize oneself with them. Therefore, the idea of radians being a requirement to his daily life through his work (past or present) is not necessarily the case. It may have been a topic he had recently read and so decided to utilize the measurement of radians in his Mount Diablo code. Despite highlighting this point, it is clear that the Zodiac Killer through his communications with the newspapers, did exhibit good "mental mapping" skills in relation to the environment around him. His compass skills were correct in all instances, whether by use of a map or through an extensive knowledge of the locations he murdered in. 

The Zodiac Killer stated correctly that "the girl was on her right side feet to the west" regarding the murder of Betty Lou Jensen at Lake Herman Road. He was correct in his payphone directions after the attack at Blue Rock Springs, stating "If you will go one mile east...... On Columbus Parkway to the public park, you will find the kids in a brown car". The Zodiac Killer was aware of the Volkswagen Karmann Ghia at Lake Berryessa being north of Park Headquarters. He showed his "cardinal points" awareness  in the November 9th 1969 'Bus Bomb' letter, describing his exit through the park of "The dogs never came with in 2 blocks of me + they were to the west + there was only 2 groups of parking about 10 min apart then the motor cicles went by about 150 ft away going from south to north west". All this, along with the use of radians in the Mount Diablo map pinpointing Ingleside Police Station and the Southern Freeway as his supposed bomb target, should give you pause for thought when the Zodiac Killer identified "Washington St and Maple St" as the location of the Paul Stine murder.   

When you factor in the cryptic directions given in the Pines and Monticello cards, it becomes increasingly likely that the Zodiac Killer had a keen interest in maps, the surroundings in which he lived and worked, along with the hunting grounds he chose for murder. It may suggest that he methodically planned out these attacks well in advance, so as to facilitate the best possible chance of escape. Taking this all into consideration, it now becomes a much more reasonable argument to suggest that the Zodiac Killer may have had prior and extensive knowledge of radians, rather than just a passing whim prior to his mailing of the Button letter on June 26th 1970.

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.