When the Zodiac Killer mailed the 408 cipher on July 31st 1969 he claimed it would reveal his identity---and backed this up somewhat by stating in his August 4th 1969 "Debut" letter that when police cracked the code they would "have me". The Zodiac Killer wasn't actually lying in this instance, because the decoded message contained both words in the following sentences: "the best part of it is that when I die I will be reborn in paradise and all the I have killed will become my slaves" and "to kill something gives me the most thrilling experience". It may be the case that the Zodiac Killer was just playing a joke on law enforcement by saying they would "have me"---giving them the personal pronoun of "me", which he amusingly used as his identity. It also appeared on the final 24th line of gibberish.

​The next time the Zodiac Killer addressed the police regarding a mailed cipher would be on April 20th 1970, when he again asked the police whether they had cracked the code, by stating "have you cracked the last cipher I sent you?" (meaning the 340 cipher). Placing this question before "My name is" appears to suggest the answer lay in the message of the 340 cipher, not the unsolved ciphertext. In other words, the answer would not only be found in the solved 340 cipher, but in the Z13 code he placed under "My name is". The answer surely had to be present in both.the Z340 and Z13---otherwise, why mention whether the previous cipher had been cracked, when he obviously knew it hadn't. When we look at the message in the 340 cipher, only one pronoun has been disproportionally overused.

If the use of the wording "have me" on August 4th 1969 was the Zodiac Killer jokingly giving us his identity as the personal pronoun of "me", then one might expect this to be more obvious when the message in the 340 cipher was revealed. If he wasn't going to give us his name in the 340 message, he would have to blatantly give us the identity of "me" in such a way that it could be interpreted. Not only would it have to be blatant, but it would have to be easily found in the 13 character cipher mailed on April 20th 1970. In the first 55 words of the 340 cipher, the Zodiac Killer excessively used the pronoun "me" five times (once every 11 words)..The Zodiac Killer's 340 message was then capped off with his crosshairs symbol, which he placed under the 20 rows of the cipher. 
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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.

All we had to do now to test the "me" hypothesis for durability, was to find the "M", "E", and possibly the crosshairs in the Z13 code. Fortunately they were there---and could be found 8 positions to the right of each "circled 8" when we circled around the cipher with a right shift. Maybe this was just a bit of luck. Then came the Halloween card on October 27th 1970, with the introductory message of "I feel it in my bones you ache to know my name. And so I'll clue you in". Conveniently positioned along the line of each word "BOO" was the word "me". One was deliberately made larger and bolder. The second peered out beyond the skeleton's left arm, which was the only part of the pasted skeleton different from the original card it was taken from. The left arm may have been misaligned to manufacture the reduction of "game" to "me". By January 29th 1974, the Zodiac Killer was probably tired of giving us clues, so decided to ram it down our throats, writing "Me-37". 

THE FOUR CIPHERS NOW HISTORY      THREE INNOCUOUS EXCLAMATION MARKS

A shift cipher with circled numbers (often seen in puzzles like escape rooms) relies on a Caesar cipher, where the secret shift key is represented by numbers wrapped inside circles, such as the three number 8's present on the simple Z13 code mailed on April 20th 1970. A shift cipher replaces each plaintext letter with another letter located a fixed number of positions down the alphabet. When you hit the end of the alphabet, the count would wrap around to the beginning. In the case of the Z13, the count of 8 would travel in a right shift and wrap around to the beginning (this would apply to the second two 8's).

This was just a continuation of the technique adopted in the 340 cipher---at the time unsolved---in which the Zodiac Killer employed a positive nine and negative eight shift to encode his message---that could be decoded with a period 19 shift. He also encoded errors into his 340 cipher using a nine shift, that became apparent as diagonal patterns across the second half of this cipher. The April 20th 1970 letter was very likely triggered by the morning newspaper reports of the Robert Salem murder in San Francisco on the same day (with Zodiac scrawled in blood on his apartment wall). A letter that had a morning postmark, so was likely created in haste with very little regard for complex cipher techniques. It is not certain that the Zodiac Killer was inspired to resume his letter writing campaign because of the Robert Salem murder, but it had been four months since the Melvin Belli letter on December 20th 1969, so this letter coinciding with his pseudonym appearing at a murder site, is probably not coincidental. 

The November 8th 1969 and April 20th 1970 letters were 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".

​That is because Edgar Allan Poe's lengthy essay "A Few Words on Secret Writing".held all the ingredients to the design of the Z340 and Z13, including the splitting of the alphabet into two halves, and the cipher wheel which adopts the forwards and backwards shifting method of encryption and decryption, involving two concentric, independently rotating circles. The bottom line is that the Zodiac Killer likely didn't have much time to dazzle us with complex cryptograms on April 20th 1970, so created a simplistic code of 13 characters in which the three circled 8's became the engine room to the solution, where we had to circle around the code to produce the joke reply to "My name is" of "ME ⊕".  

This is the answer he gave us on October 27th 1970, highlighting the word "ME" twice on the Halloween card by the clever positioning of the word "BOO", preceded again by the promise of his name through the selection of a card with the introductory message of "I feel it in my bones you ache to know my name. And so I'll clue you in". The comedic answer was "ME"--- now given to us three times. The fourth time was in plain sight on January 29th 1974, when the Zodiac gave us his "pseudonym" or "name" as "Me-37".

A further fifth clue could be found by looking at the next line in the "Tit-Willow" verse he provided in 1974. The wording "My name is" can be extrapolated from the "The Mikado" text---thereby returning us back to the April 20th 1970 letter and ""ME" once again. We have now gone full circle back to the three circled eights. We effectively have four examples of "ME" through three communications---all but one of which are sitting in plain sight. The only one hidden from view can be easily found in seconds using a simple right shift the Zodiac Killer had previously employed. The Zodiac Killer mailed at least seven ciphers during his reign of terror, but it is safe to say that the four most commonly talked about ciphers have now been finally resolved.
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FOUR AND A HALF YEARS OF ME             THREE INNOCUOUS EXCLAMATION MARKS

The Zodiac Killer employed only two pseudonyms between 1969 and 1987 in the form of "Zodiac" and "Me"---the latter of which appeared in the only known genuine mailing of 1974, when the Zodiac Killer sent the "Exorcist" communication on January 29th 1974. A signature that can easily be unearthed by taking a right shift of eight from each circled 8 in the Z13 cipher.

But it was the "Halloween" card on October 27th 1970 that again teed us up with the promise of his identity, by the Zodiac choosing a card with the introduction of "I feel it in my bones you ache to know my name. And so I'll clue you in". Knowing that this was written on the front of the card, one might have expected the Bay Area murderer to supply us with a humorous answer subtly concealed within the design of the card inner, just like "My name is" may have been followed by "ME ⊕" in the April 20th 1970 letter. This was covered extensively in a previous article, however, it appeared that the Zodiac Killer made a deliberate choice to add two exclamation marks to the "Halloween" card inner to compliment the third exclamation mark already present in the writing "But, then why spoil our game!".  The fourth was partially hidden by the the skeleton's right foot.
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In the earlier article it was shown that the Zodiac Killer placed "Peek-a-boo you are doomed" around the knothole of the tree, yet it was fashioned in such a way that the "ME" of "DOOMED" was noticeably larger and bolder than the rest of the text. The following letter "D" returned to normal size, but was followed by an oversized exclamation mark, effectively creating an emphasis on "ME!".(ME complimented by an exclamation mark). This mimicked the word to the right of the inner skeleton's left arm, which was the only part of the "cut and pasted" skeleton out of position compared to the original. The left arm had been accidentally or deliberately shifted to the right to obscure the "a" of "game" to spell "me!". This was not all.

The phrase "PEEK-A-BOO" around the knothole is positioned so that "BOO" lines up with the personal pronoun of "ME". The "D" and exclamation mark is broken off to line up with the large "BOO!" (BOO and exclamation mark) in the center of the card inner, which in turn is tilted 45 degrees anticlockwise to line up with the "me!" by the skeleton's left arm, which just happens to be the only part of the skeleton out of place compared to the original (see below). So, did.the Zodiac Killer deliberately add two exclamation marks to the card inner to form a bridge to the third, positioned after "me" by the misplaced left arm? The Zodiac Killer would have lined up "BOO" with "ME" twice (with both "BOO'S" sitting at approximately 45 degrees on the card), and fashioned "ME" followed by an exclamation mark twice. Was this a further mocking joke to compliment the simplistic answer to the Z13 on April 20th 1970? A joke that the Zodiac Killer finally got tired of on January 29th 1974, when he eventually exorcised the true identity of himself. Did anybody really expect the Zodiac Killer to give us his real name?  

On October 13th 1969 the first wanted poster was released to the public concerning the murder of Paul Stine in Presidio Height two days earlier. On January 29th 1970, the Yellow Cab Company put up a thousand dollar reward for any information leading to the arrest of the Zodiac Killer. In addition, the Teamsters Union which represents the Yellow Cab Company were reported in the San Francisco Chronicle to be considering offering a further reward on February 8th 1970 in the case of Paul Stine and Charles Jarman (another taxicab murder victim).

​Then came the murder of Sergeant Brian McDonnell (44) on February 16th 1970, who suffered devastating and sadly fatal injuries when a bomb packed with 1 1/2 inch fence staples exploded on an outside ledge of Park Police Station in the Upper Haight neighborhood. Almost immediately a reward of $5,000 was offered for information leading to the arrest of the perpetrator or perpetrators connected to this crime, authorized by Mayor Joseph Alioto on February 17th 1970, who stood on the ruins of Park Police Station and offered the money for the capture of the "maniacs" who bombed it. This total very quickly snowballed to $35,000 when the San Francisco Examiner newspaper added a further $5,000 to the reward fund. 

This devastating bomb attack on Park Police Station continued to be reported throughout February, March and April - and by April 9th 1970 the reward fund had reached $38,000, with Police Chief Alfred Nelder informing the press that four full-time inspectors had been detailed to track down the responsibles.

Therefore, it really isn't surprising that the Zodiac Killer, who threatened to bomb school buses and had a wanted poster and rewards offered for his capture, decided to piggyback off this story and begin his April 20th 1970 letter with the wording "I am mildly cerous as to how much money you have on my head now.  I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station". By invoking the murder of Sergeant Brian McDonnell, adding a bomb diagram to his latest letter, and writing "Even though I talked about killing school children with one (a bomb), It just wouldn't doo to move in on someone else's teritory", accompanied by the attribution of SFPD=0 - it was apparent that the Zodiac Killer was prepared to move his perceived bombing campaign to another district in San Francisco. The drawing of a school bus to the left of a steep embankment mirrored exactly a location just 274 feet from the San Francisco Police Department (SFPD) of Ingleside Police Station, which closely aligned with his Mount Diablo map and Z32 code. 

THE ANSWER TO THE MOUNT DIABLO CODE

The Zodiac Killer's letter may have made a subtle reference to the uncle of Brian McDonnell, Sergeant Joseph Emmett Lacey (40), who was murdered on December 30th 1956 while socializing with a friend at Eddies' Cocktail Lounge at 502 Ellis Street, San Francisco. The two were enjoying a drink when two armed men burst into the establishment with the intention of robbing it. Sergeant Lacey, despite being off-duty at the time, drew his gun and attempted to put a stop to the robbery, but was beaten to the draw and sadly killed. The April 20th 1970 communication stated that "there is more glory in killing a cop than a cid because a cop can shoot back".

Whether this was in anyway connected to the murder of Sergeant Joseph Emmett Lacey in 1956 is unknown, but its immediacy after the reference to the killing of family member Sergeant Brian McDonnell in the letter, makes it an outside possibility. The Zodiac Killer had on many occasions showed us his ability to delve into the distant past to fashion his communications.

But after mentioning it "wouldn't do to move in on someone else's territory", why would he choose Ingleside Police Station adjacent to the Southern Freeway as his next location to "rub the officers noze in their booboos"? Despite the Zodiac Killer's ability to draw from yesteryear, almost everything contained within the many Zodiac communications were often sourced from recent newspapers. In this instance, it was imperative to look through the recent publications about the Park Police Station bombing and murder of Sergeant Brian McDonnell, to see if Ingleside Police Station got a mention regarding future security measures to combat similar attacks. Any reference towards this police station may have been the only inspiration needed by the Zodiac Killer to make this his next target, and somewhat replicate the bombing attack on February 16th 1970. As usual it didn't take much searching, because Ingleside Police Stations featured numerous times in newspaper articles about the Park Police Station bombing.        

Police Chief Alfred Nelder explored the idea of installing high wire fences and floodlights around the whole of Park and Ingleside police stations, which due to tree coverage were the most vulnerable to sneak attacks and bombings. This measure would have been circumvented had the Zodiac Killer placed his bomb on a school bus route alongside the Southern Freeway---yet would still have had the devastating consequences of murdering schoolchildren within earshot and eyeline of Ingleside Police Station for maximum impact and embarrassment. The Zodiac Killer would have achieved his goal of targetting schoolchildren and a police station under the collective banner of one single attack. 

Another San Francisco Chronicle newspaper article in February 1970 reported that the previous year San Francisco police had tried out---and rejected---steel window shutters, which could have prevented the death and injury at Park Police Station. Cecil L.Ball of Ball-Bilt Millwork said he believes the bulky, heavy interior shutters would have absorbed the shock of the Park Station bombing and would have knocked down the deadly building staples which were sprayed through the air. His company put together a set of the shutters----consisting of half-inch thick steel armor plate mounted on heavy timber---which were tried out briefly at the Ingleside Police Station.   

The Zodiac Killer long claimed he was "crackproof", but he may also have proved to be "bombproof" had he placed his photoelectric cells on the embankment bordering the Southern Freeway. A countermeasure designed to target schoolchildren and the police, and render floodlights and fencing around such places as Ingleside Police Station effectively useless. The inspiration for which may have germinated in the mind of the Zodiac Killer as he read about the callous murder of Sergeant Brian McDonnell in the newspapers---who became the focus of his April 20th 1970 letter.   

In the previous article I covered William Frederick Friedman and the "CSP 888" cipher machine, a highly secure, electromechanical rotor-based cipher machine used for top-level communications during World War II. Friedman was instrumental in leading the Army's cryptologic services during the 1920s and 1930s, which set the stage for the development of secure machines like the CSP 888. There is much reason to connect Edgar Allan Poe to the design of the Zodiac Killer's Z340 and Z13 through his cryptographic works, such as Poe's July 1841 essay "A Few Words on Secret Writing", which William Friedman mentioned in his 1937 bulletin entitled “Edgar Allen Poe, Cryptographer”.

​In Poe's essay, the alphabet was split A through M and N through Z, which was seemingly adopted by the Zodiac Killer on April 20th 1970, beginning and ending his ciphertext characters with the letters A and M, in an array of characters totalling thirteen (half an alphabet). To then find the three circled 8's present in the cipher and possibly mimicking the cipher machine "CSP 888", was extremely interesting (whether deliberate or accidental). Especially when you consider that William Friedman and Edgar Allan Poe are bound together by the words in “Edgar Allen Poe, Cryptographer” (1937), written by Friedman, whose career in the field of cryptology was originally inspired by Edgar Allan Poe. Was the Zodiac Killer influenced by the cryptographic work of William Friedman, who drew upon his knowledge of this individual when he was challenged by Donald C. B. Marsh of the American Cryptogram Association inviting the Zodiac Killer to mail a cipher which truly included his name?  A challenge published in the San Francisco Examiner on October 22nd 1969, just 17 days before the Zodiac Killer mailed his infamous 340 cipher on November 8th 1969, which may also have been influenced by the works of William Friedman.

The 340 cipher was finally cracked in December 2020 by David Oranchak, Sam Blake and Jarl Van Eycke, who discovered that the cipher was a combination of substitution and transposition (using frequency analysis). The Riverbank Publications is a series of pamphlets written by the people who worked for millionaire George Fabyan in the multi-discipline research facility he built in the early 20th century near Chicago. They were published by Fabyan, often without author credit. The publications on cryptanalysis, mostly written by William Friedman, with contributions from Elizebeth Smith Friedman and others, are considered seminal in the field. In particular, Publication 22 introduced the Index of Coincidence, a powerful statistical tool for cryptanalysis. 

​William Friedman's work on transposition ciphers at Riverbank Laboratories (circa 1916–1920) established foundational, mathematical techniques for solving complex reordering ciphers. Notably, Riverbank Publication No. 19, Formulae for the Solution of Geometrical Transposition Ciphers, provided analytical methods to solve transposition, which he compared to reassembling jigsaw puzzle pieces. It's quite ironical that the title of Friedman's work was called Riverbank Publication No. 19, Formulae for the Solution of Geometrical Transposition Ciphers, when a period 19 shift was required to break the Zodiac Killer's 340 transposition cipher. This was a fraction of the work issued by William Friedman. But was he the inspiration for the Zodiac Killer, who employed this type of cipher on November 8th 1969? 

​Unfortunately, there is one final intriguing aspect to this story - and sadly it's very final. Just six days before the 340 cipher was mailed on November 8th 1969, William Frederick Friedman died of a heart attack at the age of 78. He passed away on November 2nd 1969, about a week before the Zodiac Killer's transposition cipher arrived at the San Francisco Chronicle. He was buried with full military honors at Arlington Cemetery on November 5th 1969. 

THE 888 CIPHER MACHINE USED IN WORLD WAR II

The Zodiac Killer was riding high in October 1970, currently sitting on four unbroken ciphers he had mailed on November 8th 1969, December 7th 1969, April 20th 1970 and June 26th 1970. On October 6th 1970 the Zodiac Killer would mail the 13-Hole "Punch Card" with thirteen holes punched through the fabric of the card, while simultaneously declaring himself "crackproof". His use of the words "crack" or "cracked" were usually chosen when referring to his ciphers, so one could conclude that the thirteen punch holes in the card, having been mailed 5 1/2 months after his 13-Symbol cipher on April 20th 1970, which contained the words "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is....", could be related.

​Creating thirteen punch holes in the card (previously used in coding machines), in combination with the word "crackproof", may suggest a link between the two communications mailed on April 20th 1970 and October 6th 1970. Especially when you consider no cipher was included in the card mailed in October. It has previously been shown that the 13 punch holes were positioned in a 10:3 configuration, with the 3 punch holes placed directly below where they sat in the 13-Symbol cipher on April 20th 1970 (see below). If these two communications were linked together, we need to examine the Zodiac Killer's decision to use punch holes, his choice of the word "crackproof", and his selection of the three circled 8's in his 13-Symbol cipher, to see if we can connect all three to one encipherment technique or coding machine.  

The Zodiac Killer was "about 40" years of age in 1969 according to the three sets of eyewitnesses at Presidio Heights, so he would have been around 16 (or possibly slightly older) at the time World War II ended. If he had an interest in cryptography, he would almost certainly have known about Alan Turing, a British mathematician who led the crucial World War II effort at Bletchley Park, England to crack the German Enigma machine, an electromechanical rotor device used for secure military communications. This cipher machine is arguably the most famous cipher machine in the world, but it was far from unbreakable. 

It was clear to US cryptographers well before World War II that the single-stepping mechanical motion of rotor machines (e.g. the Hebern machine) could be exploited by attackers. In the case of the famous Enigma machine, these attacks were supposed to be upset by moving the rotors to random locations at the start of each new message. This, however, proved not to be secure enough, and German Enigma messages were frequently broken by cryptanalysis during World War II. William Friedman, director of the US Army's Signals Intelligence Service, devised a system to correct for this attack by truly randomizing the motion of the rotors. His modification consisted of a paper tape reader from a teletype machine attached to a small device with metal "feelers" positioned to pass electricity through the holes. When a letter was pressed on the keyboard the signal would be sent through the rotors as it was in the Enigma, producing an encrypted version. In addition, the current would also flow through the paper tape attachment, and any holes in the tape at its current location would cause the corresponding rotor to turn, and then advance the paper tape one position. In other words, the punch holes were a key ingredient to the encipherment process. link.

SIGABA (also known as the ECM Mark II) was primarily developed by a team of American cryptographers in the mid-1930s, with key contributions from William Friedman. The device was an electromechanical rotor-based cipher machine developed in the late 1930s in the United States as a joint effort of the US Army and US Navy  At the time it was considered a superior cipher machine, intended to keep high-level communications absolutely secure. It was used throughout WWII and was so reliable that it was used well into the 1950s, after which it was replaced by newer machines like AFSAM-7 (KL-7). As far as we know, SIGABA was never broken by Axis powers. In other words it was the primary encryption technique used in World War II by America - and to the best of our knowledge - remained "crackproof" throughout its service.

This gives us the "punch holes" in paper and the "crackproof" elements, but where do we find the "888" present in the 13-Symbol cipher, that was possibly highlighted in the 13-Hole "Punch Card"? The U.S. Army called the cipher machine SIGABA or Converter M-134. The U.S. Navy called the machine the CSP-888 (Cryptographic Security Publication) and CSP-889. The machine has three banks of 5 rotors each. The main bank (at the rear) holds 5 rotors with 26 contacts each. These are the main cipher rotors. They work in a similar way as the rotors of the con­temporary German Enigma machine.

The 13-Symbol cipher on April 20th 1970, many believe was a response to the challenge by 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". 

By invoking the name of Edgar Allan Poe, it was probably hoped that the Zodiac Killer would use one of the cryptographic techniques described (or used) by Poe in his famous works, such as "A Few Words on Secret Writing", which contained 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 uncovers a potential message in the Z13 code. The SIGABA cipher machine has room for three rows (or banks), of five cipher wheels each.

​In total, we have 13 punch holes and 13 ciphertext characters, a famous "crackproof" cipher machine and the same declaration by the Zodiac Killer on October 6th 1970, the 10:3 configuration on the "Punch Card" possibly highlighting the position of "888" as the key in the April 20th 1970 letter, the CSP-888 cipher machine used by the U.S. Navy in World War II, the cipher wheel explained by Edgar Allan Poe in July 1841 in A Few Words on Secret Writing, prompted by cryptographer Donald C. B. Marsh in a newspaper article on October 22nd 1969, and the signature of "ME⊕" revealed in the Z13 by using three right shifts of 8, which was also present in the Exorcist letter on January 29th 1974. The other possibility, is we have nothing. 

`` Edgar Allan Poe (1809–1849) popularized cryptography in the 1840s through stories like "The Gold-Bug," prompting a young William Friedman (1891–1969) to pursue the field. While Friedman became a legendary U.S. Army codebreaker who valued Poe’s role as a catalyst, he famously critiqued Poe’s actual cryptanalytic skills as amateurish in his 1936 analysis, "Edgar Allan Poe, Cryptographer". Could we therefore have a crossover between the cipher machine CSP-888 and the essay of Edgar Allan Poe, A Few Words on Secret Writing, manifesting itself on April 20th 1970? A Few Words on Secret Writing is mentioned by William Friedman on page 146 of his analysis (see below).  

​​William F. Friedman on Edgar Allan Poe
THE FRIEDMAN LECTURES ON CRYPTOLOGY

FOLLOW UP ARTICLE: A FEW DAYS AFTER DEATH 

On September 25th 1990, the Zodiac Killer mailed the Celebrity Cypher to the Vallejo Times-Herald, very likely responding to the Sally Jessy Raphael TV Show featuring Robert Graysmith and Pam Huckaby, which aired a few weeks earlier. This postcard, written largely in code, suggested an introductory message, a name and a return address  But before the name (or more likely a pseudonym) of 13 characters (5 and 8) we have three coded words of 2, 4 and 2 characters, very reminiscent of the April 20th 1970 "My name is" letter.

​It is with little doubt that this was the intention of the sender. This meant that the ciphertext character "M" was represented by itself, and the fourth word in the message sequence of seven words, was likely two letters in length (one hidden beneath the stamp). If this had been designed as only one word (either "I" or "A") then the next word in the sequence becomes problematic. Bearing in mind who appeared on the Sally Jessy Raphael Show, it would be reasonable to conclude that the sender was addressing Pam Huckaby by coding the words "To Pam from me, my name is" or "To you from me, my name is". Once the letter M's were placed into the cryptogram below, the introductory message becomes very limited. 

Just after the television show, the Vallejo Times-Herald released a comprehensive newspaper article about Pam Huckaby, mentioning that she had received cryptograms and zodiac signs at her home in Antioch, entitled "Zodiac victim's sister says killer is after her". So it's not surprising that a few weeks later the Vallejo Times-Herald received a cryptographic correspondence from the killer, that may have included her name.

In my recent articles I have presented a case that the Zodiac Killer jokingly gave his name as "ME ⊕" ("ME" followed by the Zodiac crosshairs) in his April 20th 1970 letter. And here in 1990, we possibly have a message of "To Pam from me, my name is" or "To you from me, my name is". The Zodiac Killer could have been jokingly referring to himself as "me" yet again, followed by "my name is", to remind us what was present in the code on April 20th 1970.

​A few months later, somebody masquerading as the "Scorpion" mailed several cryprograms to John Walsh, host of the TV show "America;s Most Wanted", one of which was headlined by "Hi, Remember me". Therefore, we have two sets of cryptographic mailings in response to two TV shows in 1990 and 1991 (just like the Zodiac Killer did when he responded to the Jim Dunbar TV show in 1969), and mailed the 340 cryptogram to the San Francisco Chronicle. Three TV shows and three cryptograms, headlined by "I hope you are having lots of fun trying to catch me", "To Pam from me, my name is" or "To you from me, my name is" (maybe). and "Hi, Remember me".

EXTRA READING:  Four and Half Years of Me and The Identity in the Halloween Card 

​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"

The Zodiac Killer, having witnessed the young girl in the film being possessed by a "thing" inside of her, as he had claimed several years earlier by writing "help me" to Melvin Belli three times, must have been influenced by the writing on Regan's torso in one particular gruesome scene, when the words "help me" appeared on the young girl's skin, as her inner soul pleaded to be free from the force that had invaded her body.

​And you wonder why the Zodiac Killer, who mentioned The Exorcist movie in this letter, changed his signature to "Me" at the foot of the communication. He obviously altered his signature for a reason. The immediate correspondence after the Melvin Belli letter, stating "help me" three times, was mailed on April 20th 1970 and has been shown to contain the signature of "Me" by employing a simple right shift of eight. 

​But after mocking the 1973 movie by writing "I saw + think "The Exorcist" was the best saterical comidy", the Zodiac Killer completely switched to the Japanese themed theatre production of The Mikado by adding a verse from Tit-Willow (and the Japanese style symbolism). Why would the Zodiac Killer introduce this apparent dichotomy into his communication? In one scene from The Exorcist movie, Father Damien "Demis" Karras, one of the main protagonists in the 1973 film, enters the language laboratory with his tape recordings of Regan's "demonic voice" for analysis. Above the door is the word TASUKETE written on a poster. This is a Japanese word meaning "Help Me" or "Save Me". This poster foreshadows the "Help me" message that appears on Regan's body in the next scene of the film.

​The Zodiac Killer added this verse from Tit-Willow by introducing it with "yours truley", The signature of "yours truly" simply means "me". The next line of the Tit-Willow verse, which the Zodiac Killer didn't write on the Exorcist letter, contained the phrase "My name is". An introduction that gave us the 13 character code on April 20th 1970, which has been shown to contain the signature of "Me", just like the Exorcist letter, which featured The Exorcist movie and "help me" on the girl's torso, that mimicked the Melvin Belli letter on December 20th 1969.

In The Exorcist (1973), the phrase "me" relates to the demonic entity possessing young, Regan MacNeil, who claims to be the devil ("I am the devil himself!") and often uses "me" in threats, demands, and insults, particularly toward her mother, Chris MacNeil, and the priests during the harrowing exorcism rituals, revealing the entity's powerful, blasphemous identity. It's a core part of the possession, highlighting the internal struggle and the demon's contempt for humanity. 

• Identity: The demon (using Regan's voice) asserts its divine status, saying, "I am the devil himself!".
• Blasphemy: It uses "me" in conjunction with obscene acts, like masturbating with a crucifix, shocking the mother and priests.
• Manipulation: It taunts the priests with "Lick me, lick me!" and other vile commands, using "me" to exert control.
• Physical Manifestation: The word "ME" also famously appears scratched onto Regan's stomach, a terrifying visual cue of the demon's presence and power. 

Essentially, "me" in The Exorcist isn't just a pronoun; it's the voice of pure evil, a declaration of self from the demonic entity fighting for control of Regan's soul. ​

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"     

There are only four communications from July 31st 1969 to January 29th 1974 where the Zodiac Killer teased us with his identity or name. The letter to the San Francisco Chronicle on July 31st 1969 promised that "in this cipher is my idenity", but only gave us 18 characters that seemingly have no discernible message. The April 20th 1970 letter with a thirteen character code tempted us with "my name is". The October 27th 1970 "Halloween" card began with the message "I feel it in my bones you ache to know my name. And so I'll clue you in". And finally, the January 29th 1974 "Exorcist" letter substituted part of the "Tit-Willow" verse for a signature, by introducing the verse with "Signed, yours truley". The Zodiac Killer teased us in each instance - yet to this day - no common thread has been found linking all four Zodiac offerings together. However, the following presentation will serve up the same "identity" in all four communications. An identity (if correct)  that would clearly have been chosen as a joke.
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The first is incredibly tenuous, but it does exist. The deciphered portion of the 408 cipher mailed to the San Francisco Chronicle on July 31st 1969 gave us 18 letters of illegible text, yet within these 18 apparently meaningless letters the Zodiac Killer may have placed his signature, shown inside the yellow rectangle below. This suggestion is wholly unconvincing on its own, but hopefully the remainder of this analysis will maybe change your mind.

The April 20th 1970 "13-Symbol" code letter, I have argued had the key of 888, derived from the murderer's pseudonym in the 340 cipher (see here), which when applied to the Z13 code with a right shift of 8, gave us the signature of "ME ⊕" ("ME" followed by the Zodiac crosshairs). In other words, when cycling 8 positions to the right from each "circled 8", we get the signature of "ME" and his "gunsight" logo.

​If the Halloween card on October 27th 1970 was going to give us the answer of "ME" proposed in the 408 cipher and Z13 code, you would expect to find this word embedded in its design. Not only was the word "ME" curiously obvious in the Halloween card inner, it was present twice. The Zodiac Killer was clearly employing the eye in the knothole of the tree as himself, by surrounding the knothole with the ominous threat of "Peek-a-boo you are doomed".

But there is one striking feature about the writing on the tree. After the phrase "PEEK-A-BOO" the Zodiac Killer positions the word "DOOMED", such that the "ME" lines up with "PEEK-A-BOO" to create "PEEK-A-BOO, ME". It is definitely noticeable that the word "ME" is visibly larger and bolder than the rest of the writing, as if to place emphasis on this pronoun. The skeleton's left arm is also affixed to the Halloween card in such a manner that it separates the word "GAME" to spell "ME". The word "BOO" is written on the card inner at a 45 degree angle so that it too lines up with the word "ME".

The word "BOO" around the knothole and the word "BOO" to the immediate left of the skeleton, are both positioned in alignment with the word "ME". Was the Zodiac Killer giving us the answer of "ME" to "I feel it in my bones you ache to know my name. And so I'll clue you in"? Thereby replicating the answer of "ME" possibly given by the proposed solution to the Z13 code on April 20th 1970. And the signature of "ME" sitting innocuously within the 18 characters of the 408 cipher.

Finally, on January 29th 1974, the Zodiac Killer probably got tired of playing games and outright gave us his signature in plain sight, by writing "Me - 37". In fact, he effectively gave us the signature of "Me" (or "ME") a total of three times in the "Exorcist" letter. The first, as already explained, sat alongside his running victim count. The second was in the words "Signed, yours truley", because while it is often used in formal and semi-formal correspondence, in some specific contexts, it can also be used humorously or self-referentially in conversation to mean "myself". The signature of "yours truly" simply means "me". The third can be shown by using the "Tit-Willow" verse that followed "Signed, yours truley".

When we look at the Exorcist letter mailed on January 29th 1974, the Zodiac Killer appears to add the "Tit-Willow" verse from "The Mikado" for no apparent reason. However, the verse was preceded by "Signed, yours truley;" and may suggest that his identity of "Me" should be found somewhere within the verse. This concept hit a roadblock, until I looked up the following line from the complete song. The Zodiac Killer plagiarised the section below (marked in red) to place into his letter. The next line in the below verse (marked in blue) reads, in part, "Now I feel just as sure as I'm sure that my name Is". which the Zodiac Killer wrote on April 20th 1970 to introduce his Z13 code, that has already been shown to easily create the signature of "ME" and his crosshairs. Therefore, we have the "Exorcist" letter with a signature of "Me -37", the phrase of "yours truley" which means "me", introducing a "Tit-Willow" verse whose next line contains "my name is", that preceded the Zodiac Killer's Z13 code, which by using the three circled 8's as a mathematical tool, easily creates the signature of "ME". A "Tit-Willow" verse, by the way, which is split into three sections of eight lines, just like the 408 cipher. 

​July 31st 1969: "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife", but "in this cipher is my identity". EBEORIETEMETHHPITI.

August 4th 1969: "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".

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.

Recently I have released two articles examining the solution of "Me⊕" in the April 20th 1970 letter mailed by the Zodiac Killer, having been formulated by a combination of Edgar Allan Poe, the 340 cipher and the three 8's in the Z13 code. Further hints towards this solution have possibly been unearthed in the 13-Hole postcard mailed a few months later in October, and Exorcist letter mailed on January 29th 1974 in which the Zodiac Killer changed his signature to "Me" for the first time.

​The April 20th 1970 letter tempted us with an identity stating "My name is", the 13-Hole postcard contained 13 holes punched into the fabric of its design and the phrase "Fk I'm crackproof", the March 13th 1971 "Los Angeles" continued the theme by proclaiming "This is the Zodiac speaking Like I have allways said, I am crack proof", with the Exorcist letter again suggesting an identity might be hidden in its contents by the introduction of "Yours truley", followed by the Tit-Willow verse from "The Mikado". But crucially, the January 29th 1974 letter added the signature of "Me", that can be replicated using the three 8's from the Z13 code by employing a cipher wheel described by Edgar Allan Poe. But there is one communication nestled in between these other mailings, that also tempted us with a name, much like the April 20th 1970 letter. The Halloween card, mailed on October 27th 1970, began with "I feel it in my bones you ache to know my name. And so I'll clue you in".    

If the Halloween card was going to give us the answer of "Me" proposed in the Z13 code, you would expect to find this word embedded in its design. Not only was the word "Me" curiously obvious in the Halloween card inner, it was present twice. The Zodiac Killer was clearly employing the eye in the knothole of the tree as himself, by surrounding the knothole with the ominous threat of "Peek-a-boo you are doomed".

But there is one striking feature about the writing on the tree. After the phrase "PEEK-A-BOO" the Zodiac Killer positions the word "DOOMED", such that the "ME" lines up with "PEEK-A-BOO" to create "PEEK-A-BOO, ME". It is definitely noticeable that the word "ME" is visibly larger and bolder than the rest of the writing, as if to place emphasis on this pronoun. The skeleton's left arm is also affixed to the Halloween card in such a manner that it separates the word "GAME" to spell "ME". The word "BOO" is written on the card inner at a 45 degree angle so that it too lines up with the word "ME".

The word "BOO" around the knothole and the word "BOO" to the immediate left of the skeleton, are both positioned in alignment with the word "ME". Was the Zodiac Killer giving us the answer of "ME" to "I feel it in my bones you ache to know my name. And so I'll clue you in"? Thereby replicating the answer of "ME" possibly given by the proposed solution to the Z13 code on April 20th 1970. And the signature of "Me" he would ultimately deliver on January 29th 1974 to the San Francisco Chronicle.    FURTHER READING:

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