On December 7th 1969 the Zodiac Killer mailed a letter and code from Fairfield just hours before he phoned the Oklahoma radio station KTOK, both times imitating the caller to the Jim Dunbar TV show on October 22nd 1969. The person who mailed the letter provided crucial information in the Z38 code that showed intrinsic knowledge regarding the mechanics of the 340 cipher and its use of the knight's move in chess. In other words, the person who mailed the December 7th 1969 letter knew how to solve the 340 cipher. They knew this because they were the Zodiac Killer. The following will show how I arrived at the plausible solution of  "TRYING TIMES. SO I NEED APPOINTMENT TO GET HELP". 

Bearing in mind that the phone call to Oklahoma and the letter mailed on December 7th 1969 to the San Francisco Chronicle, were both continuing the theme of the Jim Dunbar TV show and Melvin Belli fiasco, in which the hoax caller was pleading for help, there is a strong probability that the Z38 code may contain a message along the same lines. If it did, it would almost certainly have been something the Zodiac Killer read in the newspapers on this topic, such as the article in the Los Angeles Times newspaper on October 23rd 1969, the day after the television show.
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In the 340 cipher message, decoded by David Oranchak, Sam Blake and Jarl Van Eycke on December 5th 2020, the Zodiac Killer used the headlines from the San Francisco Chronicle newspaper on October 24th 1969, which was titled over two pages, reading both "That Wasn't Zodiac, Say 3 Who Know" and "It Wasn't Zodiac, Say 3 Who Know". In his 340 message he stated "That Wasn't Me on the TV Show". The numerous references in the newspapers immediately after October 22nd 1969 about the caller saying "I don't want to go to the gas chamber", was replied to by Zodiac, who encoded "I am not afraid of the gas chamber". The Zodiac Killer would emphasize these two points in the first seven lines of the deciphered message.   ​

The news was abound with the failed meeting between the "Zodiac Killer" (Sam) and Melvin Belli at the Vincent de Paul thrift store in Daly City, later that day. The Los Angeles Times newspaper on October 23rd 1969 read "Attorney Melvin Belli in a phone booth at a San Francisco television station talking to caller who said he was the Zodiac Killer. Caller made an appointment but didn't keep it". This was the sort of the thing the Zodiac Killer may have mocked, after writing "I just need help" on December 7th 1969. There were two plus signs (+) together in the Z38 code, so I knew they had to represent the same plaintext letter, and gambled on the word "appointment". This would not only fill up a significant portion of the Z38 code, but would mean that the code ended with the plaintext letter "P". That was likely the last letter of "help", which also featured prominently in the Los Angeles Times newspaper and others. In fact, the title of the article was "I Want Help, Zodiac Caller Tells Attorney on Telephone". After placing "appointment" and "help" in the Z38 code, it allows us to form the word "to" immediately after "appointment" because of the double character (dotted circles). The phrase "appointment to get help" was then easy to work out. 

The first 18 ciphertext characters could then be filled in somewhat, with the dotted circle represented by the plaintext letter "T",  the circle with the single vertical line through it represented by the plaintext letter "I", the plain circle ​represented by the plaintext letter "E", the square represented by the plaintext letter "G", the triangle represented by the plaintext letter "O", and the slanted line​ represented by the plaintext letter "N". We were left with this.

The plaintext letters in blue on the top line looked like it could spell "times", followed by the word "so", thereby satisfying the double "L" ciphertext. So I took a gamble and placed the words into the message like so. 

The rest was pretty simple. After the word "so" I added the personal pronoun of "I", and "need" was the obvious next choice. The final part was filling in the blanks for the starting five plaintext letters ending in "G". Trying times" is a well-known phrase that one might experience, and necessitates the need for an "appointment to get help". This completed the Z38 code. Whether it is the correct solution I can't say for certain, but it satisfies the workings of a substitution cipher and has relevance to the contemporary events the Zodiac Killer was reading in the newspapers at the time, just like the message in the 340 cipher.

In cryptography, unicity distance is the length of an original ciphertext needed to break the cipher by reducing the number of possible spurious keys to zero in a brute force attack. That is, after trying every possible key, there should be just one decipherment that makes sense, i.e. expected amount of ciphertext needed to determine the key completely, assuming the underlying message has redundancy. For a simple substitution cipher, the number of possible keys is 26! = 4.0329 × 1026 = 288.4, the number of ways in which the alphabet can be permuted. Assuming all keys are equally likely, H(k) = log2(26!) = 88.4 bits. For English text D = 3.2, thus U = 88.4/3.2 = 28. So given 28 characters of ciphertext it should be theoretically possible to work out an English plaintext and hence the key. Wikipedia. 

• Simple Monoalphabetic Substitution Cipher: The theoretical unicity distance is about 28 characters. In practice, cryptanalysts typically need around 50 characters to perform reliable frequency analysis and achieve a definite solve.

FURTHER READING: "IRON" AND "DEATH" FEATURED IN TWO CIPHERS   

On October 22nd 1969 Will Stevens published an article in the San Francisco Examiner, in which Professor Donald C. B. Marsh urged the killer to contact him in code, stating "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"

Professor Donald C. B. Marsh, by invoking the name of Edgar Allan Poe, was probably hoping that the Zodiac Killer was going to use techniques mentioned or used by Poe, making any future offering by Zodiac easier to solve. The next two ciphers/codes mailed by the Zodiac Killer can be linked to Poe's 1841 essay "A Few Words on Secret Writing" from the July edition of Graham's magazine. The scytale method of decryption featured by Poe can solve the 340 cipher. The immediate next passage of  A Few Words on Secret Writing further describes cryptographic techniques, showing the splitting of the alphabet into ABCDEFGHIJKLM and NOPQRSTUVWXYZ, creating two portions of thirteen letters. The Zodiac Killer's April 20th 1970 communication was a 13-Symbol cipher beginning with A and ending with M. Edgar Allan Poe then describes a cipher wheel that can be used to give a credible answer to the Z13 code. But of course, it doesn't end there.

Not only did the Zodiac Killer use the encryption techniques described by Edgar Allan Poe, he may have embedded two of Edgar Allan's poems in the mechanics of the 340 cipher. Notable words from these two poems were visible when the cipher key was applied to the 340 cipher (before the period 19 shift was used to acquire the message). The presence of the second Edgar Allan Poe poem in the 340 cipher (after the key was applied) was highlighted by the author of the Z38 code mailed from Fairfield on December 7th 1969, who was undeniably the Zodiac Killer.

But let us deal with the first poem that was plainly visible in the deciphered 340 message, that read: I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME - THAT WASN’T ME ON THE TV SHOW - WHICH BRINGS UP A POINT ABOUT ME - I AM NOT AFRAID OF THE GAS CHAMBER BECAUSE IT WILL SEND ME TO PARADICE ALL THE SOONER BECAUSE I NOW HAVE ENOUGH SLAVES TO WORK FOR ME WHERE EVERYONE ELSE HAS NOTHING WHEN THEY REACH PARADICE - SO THEY ARE AFRAID OF DEATH - I AM NOT AFRAID BECAUSE I KNOW THAT MY NEW LIFE IS LIFE WILL BE AN EASY ONE IN PARADICE DEATH.

"To One in Paradise" was written by Edgar Allan Poe. This poem was first published as part of the short story titled "The Visionary" (later retitled as "The Assignation"). The poem was also published under the names "To lanthe in Heaven" and "To One Beloved". The title "To One in Paradise" was used in the February 25th 1843 edition of the Philidelphia Saturday Museum. This poem was written after the death of Poe's wife. He writes that she was his life and he lived for her and now he looks forward to the future where they will be together again in death. link. Now let's look for the second poem by Edgar Allan Poe. When the Zodiac Killer mailed the Z38 code on December 7th 1969, he repeated two notable segments of ciphertext from the 340 cipher. The first four ciphertext characters, and the last five ciphertext characters (shown below). 

This may not seem significant, until you consider that when the original 340 cipher was changed using the key, it created the words "IRON" and "DEATH" in these two exact positions (see below). Are we are expected to believe that when the author of the Z38 code selected these four and five sections of ciphertext from the 340 cipher, taken from the beginning and end of the cipher, he chose two legible words created by the 340 key by accident, which he should have had no knowledge of unless he was the Zodiac Killer. No hoaxer should have been aware of this fact and had the foresight to highlight these sections in the Z38 code. The person who created the Z38 code broke up the "Zodiac-like" pseudonym (ZO∆AIK) from the last row of the 340 cipher to create the word "death", something that would not have been expected from a hoaxer. The person who did this knew exactly what they were doing, because they created the 340 cipher.

It must be remembered that Edgar Allan Poe wrote "To One in Paradise" upon the death of his beloved wife, Virginia Eliza Poe. But how can "IRON" and "DEATH" introduce a second Edgar Allan Poe poem into the equation? Edgar Allan Poe wrote "To One in Paradise" about the death of his wife, but this wasn't the only poem written by Poe about the death of Virginia. The inspiration for the second poem, "The Bells", was reported as coming from his friend, Marie Louise Shew, who likened the sound of the Fordham University bell made of "iron", to "death".

​Edgar Allan Poe's poem "The Bells" uses different types of bells (silver, gold, brazen, iron) as powerful metaphors for the stages of human life, from the joy and playfulness of childhood (silver sleigh bells) through the harmony of youth and marriage (golden bells), to the panic and chaos of maturity (brazen bells), culminating in the inescapable melancholy and terror of death (iron bells). Written at the end of his life, the poem's shifting sounds and increasing length mirror the journey from youthful delight to the despair and inevitability of mortality, exploring the passage of time and its emotional toll. Edgar Allan Poe's poem "The Bells" was inspired by the sounds of bells from Fordham University's church while he lived nearby in the Bronx, New York, capturing the changing emotions of life, from youthful joy (silver bells) to despair and death (iron bells), a reflection of his own grief after his wife Virginia's passing.. Inspiration for the poem is often granted to Marie Louise Shew, a woman who had helped care for Poe's wife Virginia as she lay dying. One day, as Shew was visiting Poe at his cottage in Fordham, New York, Poe needed to write a poem but had no inspiration. Shew allegedly heard ringing bells from afar and playfully suggested to start there, possibly even writing the first line of each stanza.

I always wondered why these two prominent English words began and ended the 340 cipher after the key was applied to the original 340 ciphertext, and then highlighted by Zodiac in the Z38 code. The poems "The Bells" and "To One in Paradise" were written about the grief Edgar Allan Poe experienced upon the death of his wife, with "IRON", "DEATH" and "PARADISE" instrumental to both - which just happened to be present at the beginning and end of the Zodiac Killer's 340 cipher after the key was applied (although "one in paradice" was reversed at this point). Throw in the essay A Few Words on Secret Writing by Edgar Allan Poe, containing a technique that can solve Zodiac's 340 cipher (and a further technique that possibly influenced the design and solution of the Z13), and we have a story steeped in history. 

FURTHER READING: THE MECHANICS OF THE Z38 CODE 

​Many Zodiac researchers have contemplated whether the Z13 code mailed on April 20th 1970 contains a name or meaningful message, but extensive analysis of this cipher appears to show that neither are hidden beneath the ciphertext supplied by Zodiac. The first thing we notice when looking at the 13-character code is its symmetry. We have three alphabetical characters at the beginning and end. We have three circled 8's at positions 5, 7, and 9. And we have two non-alphabetical symbols four positions in from either side.

​This code can contain a valid name or message as shown by cryptographer David Oranchak. However, if the Zodiac Killer provided a genuine message or name of 13 plaintext characters, which creates the ciphertext scenario of three 8's, two A's, two M's and two N's, it must be considered highly unusual that when these ciphertext characters are placed alongside the alphabet (A through M) and we count the alphabetical difference between the two rows (as shown below), it produces yet further symmetry. Positions 1 to 4 and 9 to 13 gives us "03110" twice. The middle five positions gives us "05050". Therefore, we have a symmetrical ciphertext offering by Zodiac on April 20th 1970, that generates further symmetry in number form when placed alongside the alphabet.

​Using an identical technique in the 340 cipher, we took the pseudonym ZODIAC and placed it above the "near Zodiac" in the form of ZO∆AIK on the 20th row, and counted the alphabetical difference between the two rows. This generated the numbers 000888 that formed the basis of the three 8's in the symmetrical Z13 code, which produced further symmetry when placed alongside the alphabet. This was a 13-character code almost certainly inspired by the October 22nd 1969 newspaper article by Will Stevens, in which Dr. D. C. B. Marsh challenged Zodiac to give us his name in cipher form. An article in which Dr. Marsh invoked the name of Edgar Allan Poe, probably hoping that Zodiac would research and use cipher techniques outlined by Poe. The essay by Poe entitled "A Few Words on Secret Writing" contains all the ingredients used in the decryption of the 340 cipher and the design of the 13-character code, including the scytale method of decryption, the splitting of the alphabet, A throgh M and N through Z, and the cipher wheel, which finds the potential message in the Z13 code.
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See    Cracking the Crackproof.   Same Methodology Between Z340 and Z13.   Effectively a 353 Character Cipher.
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For the Z13 code to contain a random and/or spontaneous message, we would have to believe that all of the above scenarios were created by sheer happenstance. The only reasonable way the Zodiac Killer could have formulated these interlocking occurrences between the 340 cipher, 13-character code and Edgar Allan Poe, is if his message on April 20th 1970 was anything but random. It had to be a decipherment of simplicity, in which the majority of his ciphertext characters were chosen for the sole purpose of manufacturing this web of symmetry, not to create a plaintext message (or name) of 13 characters. 

The only constraints the Zodiac Killer faced when constructing the Z13 code, was beginning it with the ciphertext character A and ending it with the ciphertext character M, to allude to Poe. It was then a simple task of adding the three circled 8's, along with the ciphertext character E and the crosshairs, in such a position that a right shift of eight from each circled 8 (across and around the code) created the message of "ME ⊕". A message that was further explored in Four and Half Years of Me and The Identity in the Halloween Card. ​The A, M and three circled 8's all produced a numerical shift of zero when placed alongside the alphabet, allowing the Zodiac Killer to add the "E" and "⊕" (to complete the message) and manufacture the remainder of the code with symmetry in mind.

EXTRA READING: THE DEMON INSIDE OF ME 

One puzzling aspect of the Zodiac Killer's 340 cipher is his decision to separate the encipherment into three parts of 9, 9 and 2 rows, rather than simply dividing the cipher into two parts. The third section of two rows didn't follow the same technique as the other two parts. Therefore, one could conclude that it was important for the Zodiac Killer to separate the cipher into two equal parts of 9 rows, leaving the final 2 rows for an entirely different purpose, such as his signature on the 20th row. If we assert that the "near Zodiac" signature (ZO∆AIK) on the final row was a deliberate choice and not accidental, it may follow that this misspelling of "Zodiac" was purposely designed as a key.    

When we place the correct spelling of "ZODIAC" above the "near Zodiac" of ZO∆AIK, and count the alphabetical difference, the Z to Z requires a 0 shift, the O to O requires a 0 shift, and the D to ∆ requires a 0 shift, giving us three zero's. But when we look at "IAC" to "AIK", we require three shifts of 8, giving us three eight's (which when combined, gives us the three circled 8's seen in the Z13 code). Therefore, we have a 340 cipher split downwards into three parts of 9, 9 and 2 rows, with a "near Zodiac" signature on the 20th line that easily gives us three circled 8's.

​If we apply the same technique across the Z13 code, and cycle around the ciphertext to the 9th, 18th and 20th positions (9, 9 and 2), it again completes the 888 signature (shown below)..The 20th position of the Z340 and Z13 puzzles both highlight the 888 signature of Zodiac. When we apply the three shifts of 8 found by comparing ZODIAC to ZO∆AIK into the Z13 code, we get "ME ⊕" ("ME" followed by the Zodiac crosshairs)​. Two of the signatures used by Zodiac to identify himself in his letters. This has been pointed out previously by the use of "Me" as his signature within the Exorcist letter on January 29th 1974.  

In David Oranchak's excellent YouTube video entitled Let's Crack Zodiac, the 340 Cipher is Solved, he stated "The message doesn't really say a whole lot, it's more of the same attention seeking junk of Zodiac. We were disappointed that he didn't put any personally identifying information in the message, but we didn't expect him to. Maybe his name really is in the thirteen character cipher sent almost six months after the 340. Unfortunately there is not much hope of confirming any solutions for such a short cipher without getting lucky and discovering new evidence". 

I believe the personally identifying information in the 340 cipher is the "near Zodiac" on the 20th line, that gave us the three circled 8's present in the Z13 ciphertext, which produced "ME" and the "crosshairs" by employing a simple right shift of eight. The Zodiac psuedonym has been shown to be inextricably linked to the three 8's. thereby giving us "Zodiac", "Me" and the "crosshairs" in the Z13 code. The Z13 code is believed by many Zodiac researchers to be too short to solve, but by combining it with the 340 cipher it effectively becomes a 353 character cipher, where traveling 9, 9, and 2 downwards and across in both Z340 cipher and Z13 code, ultimately finds the key of 888. Which we can then apply using three right shifts of eight to reveal two further identities of "ME" and "⊕".


FURTHER READING: SAME METHODOLOGY BETWEEN Z340 AND Z13
                                     FOUR AND A HALF YEARS OF "ME"

In a recent article entitled Four and a Half Years of Me I came to the conclusion that the 13-character cipher was likely done in haste, and the Zodiac Killer jokingly provided his name as "ME ⊕" ("ME" followed by the Zodiac crosshairs), which I showed to be also present in the 408 cipher, Halloween card, Exorcist letter, and maybe was hinted at in the Eureka card. To achieve the "ME ⊕" identity, all we had to do was apply a "period 8" right shift to each circled 8 and cycle around the cipher, exactly the same methodology that was used in the 340 cipher five months earlier, where a "period 19" right shift was needed to decode his message.  .  

Many have speculated that the Zodiac Killer's opening wording in the April 20th 1970 letter of "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....", indicated that we needed to solve the 340 cipher to give us a clue to decoding the 13-symbol cipher. I have put forward that the Z13 may have revealed two forms of Zodiac identity in "ME ⊕", by using the three circled ​8's in the cipher. But how can we prove that this was the Zodiac Killer's intention? How can we prove that this was the Zodiac Killer's key? Did the answer lie in the decoding of the 340 cipher?

If the 340 cipher had been solved before April 20th 1970, we would have known that the Zodiac Killer split his cipher into three parts of 9, 9, and 2 rows. These three parts were comprised of row 1 to row 9, followed by row 10 to row 18, and finally the last two rows up to the 20th line. The Zodiac Killer gave us the key to the 340 cipher by splitting it into a 9, 9, 2 configuration. We then had to apply the "period 19" right shift to make the message possible. This configuration of 9, 9, 2 went down the cipher, so let's apply the same methodology to the Z13 by going across the cipher.

If we travel from position 1 to 9, we land on the right circled 8. If we travel from position 10 to 18, we land on the left circled 8. If we travel from position 19 to 20, we land on the middle circled 8. The configuration employed in the 340 cipher gave us the key to its solving. Does the same configuration applied to the Z13 gives us a clue to its solving? It gives us the three 8's. Once the configuration (of three parts) was identified in the 340 cipher, the "period 19" right shift was applied. Once the configuration (of three parts) was identified in the Z13 cipher, the "period 8" right shift was applied to get the message. The "period 19" right shift in the 340 cipher was crucial in finding the message. The "period 8" right shift in the 13-symbol cipher was crucial to finding the message of "ME ⊕". A personal pronoun that is seen twice in the Halloween card, and clearly written as the Zodiac Killer's identity on January 29th 1974 in the Exorcist letter.

The Zodiac Killer may also have highlighted these three circled 8 positions in his 13 punch holes in the October 6th 1970 "Pace" postcard. 

ADDITIONAL READING: FOUR AND A HALF YEARS OF "ME"     

This is a further examination of the 18 characters at the foot of the 408 cipher mailed on July 31st 1969, and the reasoning behind the apparent filler that made little sense. It is fairly clear that the Zodiac Killer made an error when converting his draft message into ciphertext form when he transitioned from the San Francisco Examiner to San Francisco Chronicle portion of the cipher, inadvertently missing out one line of 17 characters. This left him with the option of maybe dumping something unplanned into the remaining 18 characters to play a joke on the audience, which I have explored in the April 20th 1970, October 27th 1970, January 29th 1974 and December 1990 communications, found in an article entitled Four and a Half Years of "Me". 

​The word "ME" can be reasoned to be present in all the above four communications, but is also noticeable within these 18 characters, albeit not currently supported by the most convincing of arguments. So let's examine the 408 cipher in more depth, because on August 4th 1969 the Zodiac Killer informed the police to "cheer up", who would, once they solved the code "have me". This is despite his message in the 408 cipher stating that "I will not give you my name". The notion being that the identity he supplied was "ME", just like he eventually gave us in the "Exorcist" letter on January 29th 1974 when writing Me-37. The Zodiac Killer may not have been lying when he told police they would "have me" when they cracked the code. Below in green I have highlighted the characters that have seemingly been sourced by the Zodiac Killer from the columns above the final line. This final 24th row has 12 characters from the above columns, with 5 characters absent from the above columns. That is a strike rate of 70.5%. So if the final row really was just filler, why did the Zodiac Killer abandon this technique nearly 30% of the time? ​

Using the full 18 characters, let us examine the 11 characters either side of the run of 7 characters boxed in green. The first 6 characters only have a strike rate of 50% from the columns above, with the final 5 characters having a strike rate of just 40%. So its fairly obvious that the Zodiac Killer wasn't stringently harvesting characters from the above columns in these sections of the cipher. Therefore, if we discount the seven characters in a row, the remaining 11 only generate an overall strike rate of 45% from the above columns. But of these 7 consecutive characters found in the above columns, it is the grouping of 4 on row 8 that carry the most significance. The grouping of 4 characters on the eighth row spelling METH contain the object pronoun of "ME", which is visible on the final row - and an "identity" that the Zodiac Killer promised to give us in the cipher when he wrote to the San Francisco Chronicle on July 31st 1969. One could conclude that a promise to give us his identity when writing to the San Francisco Chronicle and supplying us with the third portion of the cipher, meant we would find his identity in the final 8 rows of the 408 cipher (or possibly the final line). On August 4th 1969 the Zodiac stated "By the way, are the police having a good time with the code? If not, tell them to cheer up; when they do crack it, they will have me". The final 8 rows of the cipher did contain "HAVE", "ME" and "ME".

The phrase "yours truly" has two main uses in English: as a formal sign-off in a letter and, informally and often humorously, as a substitute for "I" or "me"..When used in conversation or informal writing, "yours truly" is an idiomatic expression used to refer to oneself, the speaker or writer, usually in a self-deprecating or ironically boastful way. It functions as a first-person pronoun substitute. This is why it's important to note the use of "yours truley" and "Me" as the Zodiac Killer's chosen identity in the Exorcist letter on January 29th 1974. He effectively gave us "Me" twice. After he wrote "Signed, yours truley" in the 1974 letter he gave us a "Tit-Willow" verse from "The Mikado", whose very next line contained the phrase "My name is", which was previously followed by a 13-character code on April 20th 1970. A code which can easily be shown to give us the personal pronoun of "Me" (and the crosshairs) by employing a simple right shift of 8 positions from each circled 8.  It can be argued that he gave us two identities on April 20th 1970 by supplying us with both the "crosshairs" and "ME".

We also had the visible presence of "ME" and "me" in the Halloween card on October 27th 1970, which was teed up with the introduction of "I feel it in my bones you ache to know my name. And so I'll clue you in". The Zodiac didn't give us his name on October 27th 1970, but he did give us the personal pronoun of "Me" twice. The third portion of the 408 cipher (shown above) stated that he would not give us his name, although he did, once again, give us "ME" two more times. Throw in the autobiography of Groucho Marx entitled "Groucho and Me" with respect to the Eureka card in 1990, and it appears that the Zodiac Killer may have been playing a running joke on his audience for upwards of twenty-one years. 

After noticing the presence (or inference) of "ME" at least six times on April 20th 1970, October 27th 1970 and January 29th 1974, all with the promise or suggestion of his name or identity, this has been a retrospective analysis of the 408 cipher, looking for the most reasonable way the Zodiac Killer inserted "ME" into the final portion of the 408 cipher, mailed to the San Francisco Chronicle on July 31st 1969, and followed with a promise by the Zodiac Killer to "have me" on August 4th 1969 when the code was cracked. This analysis of the 408 cipher is far from satisfactory, but I believe our focus should be squarely on the four consecutive characters on the eighth line, which appeared like a deliberate choice by the Zodiac Killer to drop into the signature line of his three-part cipher. However, I would be surprised if there wasn't more to it.

FOUR AND A HALF YEARS OF "ME"        THE AUTOBIOGRAPHY OF GROUCHO MARX

If you want to read an introductory article to better understand the following presentation, please click here. ​

When the Zodiac Killer mailed the "Little List" letter on July 26th 1970 he pretty much gave us the full solution to the Z32 by writing "P.S. The Mt. Diablo code concerns Radians + # inches along the radians". The solution contained "radians" and "inches", and all we had to do was precede each with a number, giving us the answer of "four radians and five inches". The location of his claimed bomb was never going to land on a round number, so the solution was just an estimate, giving us the complete answer of "estimate: four radians and five inches" (supplied by Andrew Gray). That is really all there is to it. 

In the "Button" letter mailed on June 26th 1970 the Zodiac Killer wrote "the map coupled with the code will tell you where the bomb is set". We have the code answer of "four radians and five inches", but we needed to couple it with the map "set to magnetic north" of 17 degrees in 1970. That is 4 X 57.3 degrees (one radian) + 17 degrees = 246.2 degrees. Therefore, the bomb was claimed to be set at 246.2 degrees from Mount Diablo (which was an estimate). The actual target was Ingleside Police Department by the Southern Freeway, which was positioned at 251 degrees  The margin of error over a 360 degree circle was just 1.3%. That is pretty damn accurate. The crosshairs with the bold, black circle on the "Little List" letter was set to 246.2 degrees and had SFPD aligned next to it, so it's clear that the target was a police station. 

The repeating ciphertext characters are now satisfied, but do we really believe that the extremely clever Zodiac Killer added the remaining 26 ciphertext characters by using random letters and symbols that meant absolutely nothing? The solution thus far gave us 246.2 degrees (which was an estimate), but what was the real value in degrees to pinpoint the exact target? What can we possibly do with 32 characters, of which 29 are unique? If you are approaching this based on techniques employed in the 340 and 408 ciphers, then the answer is absolutely nothing. Therefore, it's fairly obvious that the Zodiac Killer used a different approach. A simplistic approach as old as time. However, the only clues we had was "P.S. The Mt. Diablo code concerns Radians + # inches along the radians" and "the map coupled with the code will tell you where the bomb is set". We have already explained both of these messages from the Zodiac Killer, so one of them must have a double meaning with respect to finding the exact location the Zodiac Killer was claiming for his bomb.

If we look at the message in blue, we already have the "map" element of "17 degrees magnetic north" (as mentioned above), so did the Zodiac "couple" this with something other than four radians in the "code", to give us the remaining degrees and pinpoint the exact location of the proposed bomb. The only way to attempt this, is by attributing number values to the alphabetical letters (correctly aligned), of which there are 20 in the code. For example A=1, B=2, C=3, etc. What are the chances that these alphabetical letters would add up to 234 in the "code", to be "coupled" with 17 degrees from the "map", and give us 251 degrees to identify the exact location of the Ingleside Police Department (SFPD) from Mount Diablo? They did.

We have "four radians" in the code (229. 2 degrees) coupled with the map of 17 degrees magnetic north = 246.2 (estimate).
We also have 234 degrees in the code, coupled with the map of 17 degrees magnetic north = 251 (the exact target location).
​The idea that the Zodiac Killer gave us 29 different characters in the Z32 with seemingly no hope of a solution, should be flipped on its head. In other words, the fact that he deliberately engineered such an impossible code with no chance of a resolution, meant that there probably was one. I expect that he thoroughly enjoyed the notion of a "crackproof" code, when in fact, the solution was anything but.  If you look too deep into a problem, you will often overlook the shallow. 
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ADDITIONAL READING: THE ANSWER TO THE MOUNT DIABLO CODE 

There may have been a change in the Zodiac Killer's approach to encrypting his ciphers/codes after the 408 and 340 cryptograms, in that the Z13 and Z32 were specifically designed with maybe just six characters forming the bedrock of each solution, but with a key of just three characters. The key characters in the April 20th 1970 letter were the three 8's, whereas the key characters in the "Button" letter Z32 code on June 26th 1970 were the three repeating symbols of C, O and the triangle. These three symbols (characters) were seemingly the key to unlocking both codes mailed on April 20th 1970 and June 26th 1970, with the remaining characters beyond the total of six possibly meaningless filler placed around them.

Once the Zodiac Killer had supplied us with the prompt of "The Mt. Diablo Code concerns Radians & # inches along the radians" on July 26th 1970, the placement of "four radians and five inches" into the Z32 from position 9 to 32, unlocked the answer of "estimate" from position 1 to 8, to identify the complete solution of "Estimate: four radians and five inches". There was a total of six characters at play here, but only three were key characters involved in the solution. The key characters in the Z13 on April 20th 1970 were the three circled 8's, but a total of six characters may also have been at play here. They were the three 8's, and the "M", "E" and "crosshairs". If the proposed solution of "Me⊕" for the Z13 is correct, then both the Z13 and Z32 codes follow the same template.   

It can be seen above in the Z32 that six characters are at play here, but only the three characters at positions 14, 26 and 32 are key to the solution. The characters at 14, 26 and 32 within "four radians and five inches", unlock the characters at positions 1, 2 and 6 to give us the word "estimate" and complete the full solution. In the Z13 below we again have six characters at play, but only three characters at positions 5, 7 and 9 are key to the solution of "Me⊕".    

This drives at the heart of the question, of whether the Zodiac Killer used redundant characters in 54% of the Z13 and 81% of the Z32 to change the methodology he employed in his previous ciphers. If the proposed solution to the Z13 is correct, then there is a good argument to be had that the Zodiac Killer used only six functional characters in both designs, of which, only three were key to each solution. That key being the three circled 8's in the Z13, and the C, O and △ in the Z32.

The April 20th 1970 letter opens with "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....". One of the takeaways from the mention of his previous cipher while beginning this communication, has been that something about that previous cipher may aid in the solving of the current Z13 code. Many have taken the code key from that now solved 340 cipher and tried to apply it to the Z13 code. While some of those attempts have produced interesting outcomes, they have all required some form of manipulation to generate a desired result, which leaves room for objection. But what if the answer or key lay in the unsolved 340 cipher at the time Zodiac mailed his Z13 code on April 20th 1970. Bearing in mind this latest letter was suggesting that the Z13 code would reveal a "name" or "identity", it is quite possible that his identity in the unsolved 340 cipher held the clue.

In the 340 cipher on the final line he appeared to give us his signature of ZODIAC from characters 333 to 338. However, he replaced the "D" with a blackened triangle, reversed the "I" and "A", and changed the "C" for a "K". Despite this, it's unmistakable presence is there for all to see. What if we took this identity to solve the Z13 code.  

As stated previously, Professor Donald C. B. Marsh invoked the name of Edgar Allan Poe to challenge Zodiac to reveal his name on October 22nd 1969, hoping that the Zodiac Killer would utilize the cryptographic works of Poe to create any forthcoming ciphers. Taking one look at Poe's essay, "A Few Words on Secret Writing" in the July edition of Graham's magazine, you can see the scytale method of decryption that can be used to solve Zodiac's 340 cipher, the cryptographic technique of splitting of the alphabet A through M and N through Z, which Zodiac employed in his design of the Z13 code, and the cipher wheel explained by Poe, which not only decodes the "near Zodiac" on the final line of the 340 cipher to give us the key, but provides us with a resulting key that the Zodiac placed directly into his 13 characters on April 20th 1970, that generates an answer he would later reveal as his signature on January 29th 1974. That signature was "Me". 

The "near Zodiac" in the 340 cipher has simply been manipulated using a cipher wheel. When we compare the correct spelling of ZODIAC to the version supplied on the final line of the 340 cipher, we can see that Z to Z, O to O, and D to triangle generates no difference alphabetically (000). Whereas "IAC" to "AIK" generates a shift of 8 positions for each letter, producing 888. This provides us with 000888, the possible origin of the three circled 8's in the Z13 code. Visit the Caesar cipher wheel here and type in the number 8 (see below). The inner wheel will spin 8 positions clockwise so that the outer wheel "I" is represented by the inner wheel "A" (and vice versa). The outer wheel "K" is represented by inner wheel "C" (and vice versa). This is the bedrock of the switch from "IAC" to "AIK" in the spelling of ZODIAC. If we place the 13 characters from the April 20th 1970 letter within a cipher wheel (shown above), forming an inner and outer ring, and then spin the inner wheel clockwise by 8 positions, the three circled 8's land over "ME" and the "crosshairs". The signature he chose to use in the "Exorcist" letter on January 29th 1974, created by a technique described by Poe in "A Few Words on Secret Writing".    

But how do we know that the three circled 8's are the key to solving the Z13 code? In the April 20th 1970 letter the Zodiac Killer wrote "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....", followed by 13 characters. The next time the Zodiac used the verb "to crack", is when he told us he was crackproof in the 13-Hole postcard at the beginning of October 1970, five and a half months later. The Zodiac Killer stated "Fk I'm crackproof" and punched 13 holes into the fabric of the postcard. But just like the April 20th 1970 letter featured three circled 8's in a configuration of 13 characters, the postcard in October separated out three punch-holes from the other ten. These three punch-holes were positioned almost directly below the positions the three 8's slotted into the Z13 code (see below). In other words, pull the three 8's downwards from the Z13 code and you get the 10:3 configuration shown in the 13-Hole postcard.  

Was the Zodiac Killer highlighting the three punch-holes (888) from the total of 13 to show that these were the key to solving the "crackproof" Z13 code on April 20th 1970? In total, we have the three circled 8's generated by a cipher wheel from the "near Zodiac" in the 340 cipher, placed into the Z13 code five months later, which by using a cipher wheel once again, generated the signature of "Me" from the Z13 code, that is present as the signature in the Exorcist letter on January 29th 1974. The Edgar Allan Poe essay "A Few Words on Secret Writing", featuring the cipher wheel, the scytale method of cryptography, and the technique of splitting the alphabet into 13 characters, which are all integral to the solving of the 340 cipher and the possible design of the Z13 code, may very well have been chosen because of the challenge by Marsh on October 22nd 1969. He wanted the Zodiac Killer to send a cipher to The American Cryptogram Association that would honestly include his name. The murderer of five may have given Professor Marsh more than he bargained for.

On January 29th 1974, April 24th 1978 and October 27th 1987, the Zodiac signed himself "Yours truley" or "Yours truly" as an added signature. "Yours Truly" simply means "Me". Both were used in the Exorcist letter on January 29th 1974. "Yours truly" originated as a formal sign-off for a letter, a shorter version of phrases like "I am truly yours". Today, it is mostly used in a conversational or informal context to refer to oneself in a playful, humorous, or self-deprecating manner. I believe that when the Zodiac Killer mailed the April 20th 1970 letter and Z13 code, he gave us the answer of "My name is....Me" as a playful joke. He was taking the piss.

A solution created by converting ciphertext into plaintext from just 13 characters could never be verified, which is probably why he employed a different technique, inspired by the writings of Poe in Graham's Magazine in 1841. Those three circled 8's may have stood out for a reason. 
 
FOLLOW UP ARTICLE: THE SAME IDENTITY IN THE HALLOWEEN CARD 
FURTHER READING: AN IDENTITY DISCLOSED IN TWO LETTERS 

One of the strangest offerings of the Zodiac Killer was the 32-Symbol cipher on June 26th 1970, but why did he design a cipher with 29 individual ciphertext characters and only three repeating, with practically no chance of a solution? The unusual answer to this question, is that the Zodiac Killer thought in 30 days this cipher had a reasonable chance of being solved, because he designed it in two parts. Knowing that the second part of the puzzle was to arrive on July 26th 1970, he deliberately engineered the first part with no reasonable prospect of a solution, with the answer available in the second instalment. The Zodiac thoroughly expected that once his "Little List" letter arrived at the San Francisco Chronicle on July 26th 1970, the solution to the 32-Symbol cipher would soon be discovered. However, it would take another 50 years to solve, when Andrew Gray (Druzer) forwarded me the solution on December 27th 2020.

​After the remarkable achievements of Dave Oranchak (USA), Sam Blake (Australia) and Jarl Van Eycke (Belgium) in cracking the 340 cipher earlier that month, we now had another massive breakthrough. The Zodiac had created the 32-Symbol cipher with 29 unique characters - because had he not done so - he knew that the extra clues he was going to provide on July 26th 1970 would have made it far too easy. The fact that he gave us such little opportunity to solve the 32-Symbol cipher on June 26th 1970, was effectively the evidence there was going to be further clues forthcoming. He likely knew this from the very start, which explains the difficulty of his original offering. You would only create an unbreakable cipher in June, if you knew the answer was coming down the tracks in July. The solution was so extremely simple, it was overlooked by everybody apart from Andrew Gray, Having previously identified that the only viable solution was a measurement of four radians and five inches to locate the bomb, I failed to understand that these were the measurements to be placed directly into the cipher. Fortunately, Andrew Gray was on hand to fit the final pieces into the jigsaw. The solution can be explained in three easy parts.

[1] The first crosshairs in the "Little List" letter gave us a prominent black circle positioned at four radians and magnetic north around its circumference (246.2 degrees), with the target SFPD (San Francisco Police Department) next to it. We had to travel four radians around the circle, with the zero position (from the map below left) set to magnetic north (17 degrees).
​4 multiplied by 57.3 degrees (radian value) plus 17 = 246.2 degrees.  

​​[2] The second crosshairs (see orange image below) in the "Little List" letter gave us most of the solution to the 32-Symbol cipher, where Zodiac wrote "The Mt. Diablo Code concerns Radians & # inches along the radians". He told us that the code concerned (was about) "Radians & # inches". The Zodiac didn't place a hashtag before the radians value because he had already given us that value in the first crosshairs. It was "four Radians & # inches". All we had to do now was add the inches value to where the Zodiac had placed an arrow pointing to the hashtag. 

​Despite the relatively recent explosion in popularity of the hashtag on social media, the hashtag is often used as a number sign, such as "#1" instead of "number 1", The Zodiac Killer was instructing us to insert the number five before inches. Hence his use of the hashtag. The target of SFPD (San Francisco Police Department) can only be five inches based on the Mount Diablo map scale of 6.4 miles to the inch, because this is the only amount of inches that can possibly land over San Francisco from the peak of Mount Diablo. Equally, four radians is the only amount of radians that can fall over San Francisco from Mount Diablo. We now have the answer of "four Radians and five inches". There was only ever one possible answer.   

[3] The location that Zodiac chose to identify for his buried bomb - the embankment opposite Ingleside Police Station (SFPD) - only fell close to whole radians and inches (it was 4.08 radians and 4.85 inches), so he approximated the measurements and rounded them off to four and five. An approximate calculation is an "estimate", hence the final solution of "estimate: four radians and five inches" (set to magnetic north).   

You will notice that when Zodiac placed "four radians and five inches" from positions 9 to 32 in the cipher, he repeated no ciphertext characters. From positions 1 to 8 he then selected three ciphertext characters to repeat in the word "estimate" to make the cipher solvable. This made the first word in the cipher self-evident, because this was the only word in the 32-Symbol cipher that required extra clues. The only mystery remaining, is why Andrew Gray doesn't get the recognition he fully deserves for cracking this supposedly unsolvable cipher. All the ciphers so far solved in the Zodiac case are easily explained once their mystery is unlocked - and this cipher is no different. It is a simple three step process.  

On June 26th 1970 the Zodiac Killer was telling the truth when he wrote "the map coupled with the code will tell you where the bomb is set". The code of "four radians and five inches", to be coupled with the map crosshairs "to be set to magnetic north", gave us the complete answer of "four radians set to magnetic north and five inches". The use of radians and inches on July 26th 1970 was an admission that the original letter on June 26th 1970 didn't meet the requirements for a solution to be satisfactorily achieved. The answer was ultimately embedded in three crosshairs spanning thirty days (06/26/1970 magnetic north, 07/26/1970 four radians, 07/26/1970 five inches)..

It is patently clear by now that if the 13-Symbol cipher contains a name or message, there are going to be thousands of answers that could fit into this short code, that may or may not be correct. The Zodiac Killer almost certainly knew this to be the case after designing two lengthy ciphers of 408 and 340 characters, which he knew only contained one possible decryption. He must have known that any solution of 13 characters could never be proven to be the correct answer. That is possibly why he didn't create a solution of 13 characters.

​After the challenge by D. C. B. Marsh of the American Cryptogram Association on October 22nd 1969, invoking the name of Edgar Allan Poe in his address to Zodiac to reveal his name, he must have hoped that the Zodiac Killer would employ methodology featured by Poe, such as the ones described in his famous essay entitled "A Few Words on Secret Writing". The first three cryptographic methods detailed in Poe's essay were the scytale cipher, which can be used to decode the 340 cipher. The second cryptographic method told of splitting the alphabet in 13 characters of A through M, and N through Z. The Zodiac Killer supplied us with a 13-Symbol cipher on April 20th 1970, beginning with A and ending in M. The third cryptographic method (based on the second method) described two circular pieces of pasteboard, one on top of the other, each containing 26 letters of the alphabet in 26 segments, radiating from the center. One disk was fixed and one was moveable. See here. 

​In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code, or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.

​The Zodiac Killer may have employed a variation of this technique by using a right shift of 8 in his 13-Symbol cipher, encircling the number 8 to denote the use of a Caeser Cipher Wheel. By placing a wheel or circle around the number 8 in the 13-Symbol cipher, the Zodiac Killer may have been telling us to rotate through 8 positions of the cipher to reveal his name. Of course, the Zodiac Killer was highly unlikely to give us his name, but he could have been playing one big joke. In his 148 character cipher in May 1971 the Zodiac Killer actually stated "I'll never give my name". 

It can be seen in this image that if you rotate the outer circle clockwise by eight positions from the first number 8, it lands over the M of the inner circle. The second number 8 rotated by eight positions lands over the letter E. The third number 8 rotated by eight positions lands over the crosshairs of Zodiac, giving us the following message shown below. But how can we possibly prove this was the intended message, in contrast to a name or message that used all thirteen characters. 

After nearly four years of this code being unsolved, the Zodiac Killer may have thought it time to give us the answer by mailing us the Exorcist letter on January 29th 1974, offering us the words "Signed, yours truley" followed by a verse from The Mikado's Tit-Willow. When you examine the complete verse of Tit-Willow, you will notice the immediate next sentence after Zodiac's contribution contains eight consecutive letters of the alphabet spelling "My name is". The only other place this is found is in the introduction to the 13-Symbol cipher on April 20th 1970. In other words, we can only connect the phrase "My name is" to these two communications. 

The Zodiac Killer certainly wasn't going to make it easy for us, but if the observations described above are correct, the Zodiac Killer gave us "My name is", followed by his signature of "Me - 37" in the Exorcist letter, in similar fashion to the April 20th 1970 letter, which may have given us "My name is", followed by "Me (and his crosshairs)".  In most of his communications the Zodiac used his crosshairs accompanied by a running victim total, therefore, "Me - 37" and "Me (and his crosshairs)" can be equated to "crosshairs - 37", just like his previous running victim totals. Such as the April 20th 1970 letter below. This solution to the 13-Symbol cipher can at least be replicated in a later communication, with the common signature of "Me". 

The phrase "My name is Me" is a statement of identity, often used playfully or to emphasize a unique connection to oneself. In the July 31st 1969 letter to the San Francisco Chronicle the Zodiac Killer wrote "In this cipher is my idenity". On August 4th 1969 he wrote "By the way, are the police having a good time with the code? If not, tell them to cheer up; when they do crack it, they will have me".

"Signed, yours truly, me" is a somewhat informal and often playful way of signing off a letter or email, signifying that the sender is the "me" in the message. It's used as a closing, similar to phrases like "Sincerely" or "Best wishes," but with a touch of self-deprecating humor. Informally, yours truly is also used as a synonym for I, me, or myself. Yours truly is a conventional phrase that is used to politely end a letter. It is used in the same way as similar phrases, such as Sincerely or Best wishes. ​​"Your humble servant" and "yours truly" are both valedictions, formal closings used in letters and emails to express respect and sincerity. "Your humble servant" is a more formal and historical phrase, while "yours truly" is a more common and less formal option. 

The April 20th 1970 letter with the phrase "My name is", along with its accompanying 13 character code, was very likely prompted by Professor Donald C. B. Marsh, who 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".

There is good reason to believe that the inspiration for both the Z340 and Z13 codes came from an essay by Edgar Allan Poe called "A Few Words on Secret Writing", Whatever the case, you can solve the 340 cipher using the scytale (or skytale) method of cryptography. Although Dave Oranchak doesn't believe the Zodiac Killer used the scytale method of encryption in the creation of the 340 cipher, this decryption tool does actually decode the message in the 340 cipher. The immediate cipher mailed by the Zodiac Killer after the challenge by Professor Donald C. B. Marsh was the 340 cipher postmarked November 8th 1969, so is it possible the Zodiac Killer used Marsh to create his cipher? If so, the clue to solving the 340 cipher would have been ever present at the American Cryptogram Association.  

Helen Fouché Gaines (October 12, 1888 – April 2, 1940) was a member of the American Cryptogram Association and editor of the book Cryptanalysis (originally Elementary Cryptanalysis) first published in 1939. The book described the principal cryptographic systems of the 19th century and cracking methods including elementary contact analysis (cryptanalysis). The original black and white logo of the American Cryptogram Association appeared on the cover of "Elementary Cryptanalysis: A Study of Ciphers and Their Solution" by Helen Fouché Gaines. The logo featured a scytale cipher. So, did the Zodiac Killer design and mail a cipher that could be solved using the scytale method of decryption, inspired by the American Cryptogram Association logo, from right under the nose of ​Professor Donald C. B. Marsh, the very man who challenged Zodiac seventeen days earlier. Below is the original and modernized version of the logo. The first cipher discussed in Edgar Allan Poe's  "A Few Words on Secret Writing" was the scytale cipher (scytala), present on the American Cryptogram Association logo, with both featuring in the San Francisco Examiner challenge by D. C. B. Marsh on October 22nd 1969.

The address of the American Cryptogram Association was 818 14th Street, Golden, Colorado. Here is a "Union Cipher Disk", with the address numbers of the American Cryptogram Association and the 888 present within the 13-Symbol cipher. 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". This type of encryption features in Poe's "A Few Words on Secret Writing". In fact, the first three enciphering techniques described in "A Few Words on Secret Writing" are somewhat connected to the Z13 and Z340. [1] Scytale Cipher [2] Splitting the alphabet A to M, N to Z, into two parts of thirteen characters [3] Cipher wheel/disk. Here is a working cipher wheel using the alphabet. 

MY NAME IS ARTHUR GORDON PYM - TAKEN FROM POE'S ONLY COMPLETE NOVEL
​TO ONE IN PARADISE - A POEM BY EDGAR ALLAN POE (PRESENT IN THE 340 CIPHER)

On January 29th 1974 the Zodiac Killer tempted us with his name by writing "Signed, yours truley" and then placing an extract from The Mikado's Tit-Willow verse. The implication being that the Zodiac Killer's name may be found within the verse. In 2017, I noticed that the complete Tit-Willow verse from Gilbert & Sullivan's play had the phrase "my name is" within the wording "my name isn't", reminiscent of the April 20th 1970 letter stating "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....", followed by a 13 character code.

The full Tit-Willow verse read "my name Isn't Willow, tit-willow, tit-willow", so could this have featured in the 13 character code? The Zodiac Killer could have playfully used Tit-Willow as his name on April 20th 1970, before reversing this on January 29th 1974 by invoking the Tit-Willow verse in his Exorcist letter. The proposed suggestion being "My name is only Tit-Willow". Although this solution fails by using the plaintext letters "T" and "I" to represent the ciphertext "circled 8", the three "circled 8's" can spell "TIT". One would like to believe that the Zodiac Killer - knowing his 13 character code was practically unsolvable - would have given us a clue in his later letters. So was the "Signed, yours truley" phrase, followed by "my name isn't" in 1974, that clue?   

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