On December 3rd 2020 David Oranchak, Sam Blake and Jarl Van Eycke unlocked the mystery to the 51-year-old 340 cipher, mailed by the Zodiac Killer on November 8th 1969.  The decoded message was a response to the Jim Dunbar Show in which an imposter/fraud called in to the TV show pretending to be the infamous Zodiac Killer.on October 22rd 1969. It may have also been a response to the San Francisco Chronicle article on October 23rd 1969 entitled A TV Runaround With Zodiac Calls in which "Belli told Sam he'd attempt to get a promise from District Attorney John J. Ferdon that Zodiac would be spared the gas chamber if convicted of murder". The Zodiac Killer responded in code that he was "not afraid of the gas chamber". 

The following day, the San Francisco Chronicle published another article which featured the opinions of Nancy Slover, David Slaight and Bryan Hartnell, who were the only three people credited with hearing the Zodiac's voice to date. The headline of that column read That Wasn't Zodiac, Say 3 Who Know, to which the Zodiac Killer would reply in his message in the 340 cipher by confirming "That wasn't me on the TV show". He took the newspaper headline and incorporated it into his hidden message. The Zodiac Killer was effectively rejecting the notion that the person who appeared on the Jim Dunbar Show claiming to be him was the genuine article - the caller was a fraud or imposter.

The decoded 340 ciphertext 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.

However, it didn't stop there. On February 5th 1970, the Desert Sun newspaper reported that "a man claiming to be the Zodiac killer of five persons held another on-the-air conversation today with television personality Jim Dunbar. Two police inspectors closeted themselves with Dunbar at station KGOTV immediately after the one-sided conversation, which consisted mainly of Dunbar asking questions and repealing fragments of answers". This second call was also reported in the San Francisco Chronicle on February 6th 1970, again highlighting the belief of investigators that this person was another fraud impersonating the Zodiac Killer. Just over a year later the Zodiac Killer mailed a 148 character cryptogram and letter, again encoding a contemporary message, but this time calling out Karl Francis Werner as a phony. Karl Francis Werner had just been arrested in connection with the murders of Kathie Reyne Snoozy, Debra Gaye Furlong and Kathy Bilek, two of which he had long claimed he murdered since the mailing of his November 8th 1969 Dripping Pen card and 340 cryptogram. He would also soon claim Kathy Bilek as a murder victim in the July 13th 1971 Monticello card. The Zodiac Killer was clearly upset somebody else had been arrested for the two San Jose murders on August 3rd 1969 and was responding to a San Francisco Chronicle article on April 30th 1971 entitled San Jose Student Held in Slaying of Three Girls. The newspaper article read "He was immediately advised of his rights concerning any statements he may make and legal representation to which he is entitled, the detectives said. Werner was then taken to the scenes of the crimes. Late yesterday he was undergoing questioning. The detectives would not reveal what statements, if any, he had made concerning the killings of the three girls". His response was immediate, likely firing off the following communication in early May. 

The Zodiac Killer was responding to the Paul Avery newspaper article on April 30th 1971 describing the arrest and interview of Karl Francis Werner by law enforcement, imploring investigators to "stop listening to phonys". Just like the 340 cipher, in which the Zodiac Killer used the newspaper headline banner of That Wasn't Zodiac, Say 3 Who Know to create "That wasn't me on the TV show", he would again use a newspaper headline banner in his rebuttal of Karl Francis Werner as the killer of the three girls (in particular, Snoozy & Furlong).

An imposter/fraud had called into the Jim Dunbar TV Show on October 22nd 1969, followed by a second call to the show on February 5th 1970. The San Francisco Chronicle article on the left was entitled Talk Show's Zodiac Caller Called a Phony. The article read "Homicide detectives later listened to a tape recording of the conversation and concluded that Sam was a phony. It most certainly was not Zodiac, said Inspector David Toschi".  Fast forward to May of 1971, in which Karl Francis Werner is being interviewed by investigators for three murders, including the brutal stabbings of Kathie Reyne Snoozy and Debra Gaye Furlong, to which Zodiac had previously claimed by the addition of "Aug" on his November 8th 1969 Dripping Pen card. Perceived by him, the Zodiac Killer has now had the indignity of two phone calls to the Jim Dunbar Show, where a phony has effectively claimed his crimes, followed by the arrest and interview of Karl Francis Werner in 1971, possibly being credited with crimes he had previously claimed. His response to law enforcement was "stop listening to phonys", again using a newspaper headline incorporated into the ciphertext message of his cryptogram.

At the time the Zodiac Killer mailed the 148 character cipher in 1971, the 340 cryptogram was unsolved. Yet here we have two lengthy cryptograms, both of which are incorporating in contemporary form the rejection of an imposter or phony by using the phrases "That wasn't me on the TV show" and "stop listening to phonys" - and both cryptograms incorporated the language used in two newspaper headlines.

The 340 and 148 character cryptograms are inextricably linked through a message that is contemporary in nature, both are the rejection of two people connected to his crimes (and claimed crime), and both the Dripping Pen card and 148 character cipher are indelibly linked to the murders of Kathy Reyne Snoozy and Debra Gaye Furlong who were horribly killed and mutilated on August 3rd 1969 in San Jose. The Zodiac Killer would finish his written message in May 1971 with the wording of "I will send a patch of human skin if their is some left over". This was a threat to kill another three kids, just like Snoozy, Furlong and Bilek. The nature of these three brutal stabbings (in excess of 300 knife wounds) should leave you in no doubt the meaning behind the sinister message of "I will send a patch of human skin if their is some left over".

On December 3rd 2020, Dave Oranchak (USA), Sam Blake (Australia) and Jarl Van Eycke (Belgium) finally unearthed the solution to the 340 cipher after 51 years. The message 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.
Here is what the Zodiac Killer could have written regarding the phone call to the Jim Dunbar Show:
I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME - STOP LISTENING TO PHONYS - 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. 

One of the most remarkable achievements in the Zodiac story occurred in 2020, when David Oranchak, Sam Blake and Jarl Van Eycke collaborated to finally break the 51 year resistance of the infamous 340 cipher on December 3rd. But what inspired the added complexity and the diagonal shift employed by the Zodiac Killer in his encryption technique on November 8th 1969. The trigger may have been his 408 cipher and the detailed attempt to break it in the Vallejo News Chronicle on August 4th 1969, at a time when the Zodiac Killer would undoubtedly have been scrutinizing the newspapers for progress on his 408 cipher. This was pointed out to me by the forum contributor known as Cragle, who made this astute observation recently.     

The cryptogram fan from San Francisco, a graduate student, made some observations regarding the 408 cipher (shown on the left). While his analysis wasn't wholly accurate, it is this newspaper article that may have bearings on the technique employed by the Zodiac Killer when designing his 340 cipher. On page two of this newspaper article it continued The pattern beginning to take shape apparently will end up a three-tiered diagonal structure composed of sections, of each of the three ciphers. Work with the patterns of the ciphers, which he calls complex and the work of a very intelligent person, has yielded eight doublets of symbols which are equals. He remarked that he didn't feel the ciphers were a hoax because they are too complicated and required too much effort to devise. "A computer may have been used" he said. He thinks the person who made them is intelligent, scheming and imaginative, but not really unusual. "I know kids in school who could do better" on cryptograms. 

The next communication mailed by the Zodiac Killer on October 13th 1969 promised to target young children, threatening that "School children make nice targets, I think I shall wipe out a school bus some morning. Just shoot out the front tire + then pick off the kiddies as they come bouncing out". But the most important section in the Vallejo News Chronicle article was "The pattern beginning to take shape apparently will end up a three-tiered diagonal structure composed of sections". The Zodiac Killer's 340 cipher, that followed the October 13th 1969 letter, was three-tiered just like the 408 cipher, but crucially it was structured diagonally for the majority of the coding, as postulated in the newspaper. The title of the newspaper article was Text Of Letter May Offer Clues, but did it offer the inspiration for the Zodiac Killer to create a diagonal shift in his 340 cipher just three months later?

On October 22nd 1969, the San Francisco Examiner newspaper published an article by Will Stevens, which laid down a challenge from Professor D.C.B. Marsh of the American Cryptogram Association (ACA) to the Zodiac Killer, attempting to coax him into revealing his name.

The newspaper stated "Dr Marsh told the Examiner today: "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 Allen 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 D.C.B. Marsh was probably hoping the Zodiac Killer would employ a cryptographic technique featured in the works of Edgar Allan Poe, thereby making any future cipher mailed by the Zodiac Killer easier to crack. As it turned out, the Zodiac Killer's 340 cipher mailed on November 8th 1969 could be solved using the scytale method of encryption detailed in Edgar Allan Poe's essay A Few Words on Secret Writing in the very first paragraph. This was covered extensively in the article The Inspiration Behind the Zodiac Killer's 340 Cipher. We have Professor D.C.B. Marsh of the American Cryptogram Association creating the trigger, by inserting Edgar Allan Poe into the mind of the Zodiac Killer. The Zodiac Killer then created the 340 cipher that could be deciphered using the scytale method featured in Poe's A Few Words on Secret Writing. What are the odds that one of Edgar Allan Poe's poems would partially appear in the solution to the 340 cipher?

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 25, 1843 Saturday Musuem. 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.

The breaking of the 340 cipher by David Oranchak, Sam Blake and Jarl Van Eycke on December 3rd 2020 was a fantastic achievement after 51 years, only slightly tarnished by the banality of the message encoded by the Zodiac Killer, in which he denied it was him on the Jim Dunbar Show, along with the usual paradice and slaves nonsense. However, it may have gone a long way to verifying two previous communications once considered inauthentic Zodiac letters. 

The 340 message stated "That wasn't me on the TV show", thereby suggesting by inference that the person who called into the Jim Dunbar TV show on October 22nd 1969 was an imposter and fraud. Shortly after the April 29th 1971 arrest of Karl Francis Werner for the murders of Kathie Reyne Snoozy, Debra Gaye Furlong and Kathy Bilek in San Jose and Saratoga, another cryptogram was mailed from Fairfield to the San Francisco Chronicle containing 148 characters. It too was effectively delivering a contemporary message, again claiming that the person (Karl Francis Werner) being 'interviewed' was an imposter and fraud, stating "Tis the Zodiac Speacking. Why can't you stop me. I can't stop killing. Stop listening t(o) phonys". The 340 cipher was unbroken in 1971, yet the author of another contemporary enciphered message was again claiming that the person in the spotlight was a "phony". The only difference this time was the Zodiac Killer was the "phony", falsely attempting to wrestle back the murder victims of Snoozy & Furlong on August 3rd 1969, that he had claimed in the Dripping Pen card mailed on November 8th 1969, with his addition of "Aug" in his chronological victim count of seven. He would further compound matters by adding the April 11th 1971 murder of Kathy Bilek to this list, when on July 13th 1971 he claimed her murder in the Monticello card by stating "In The Woods Dies April".

This should allay any doubts as to the authenticity of this communication, especially when you consider that the Monticello card "shought victims 21" just like the written message accompanying the 148 character cipher - and both were withheld from the newspapers.

The 340 cipher also went a long way to verifying the 38 character code, mailed from Fairfield on December 7th 1969, because both cryptograms isolated the word "death" at the end of each message. The person who created the Z38 deliberately separated the prominent ZO∆AIKꞮ+ characters on the bottom line of the 340 cipher, into AIKꞮ+ on the bottom line of the 38 character code. thereby manufacturing the word "death". Druzer, a valued contributor to both main Zodiac forums, pointed out the same thing, stating  "The most curious/compelling feats are that the author isolated actual words, most notably death, and that he refrained from copying Zodaik, which would certainly be expected of a hoaxer".  

The 340 cipher did indeed harbor a banal and relatively uninteresting message after a long 51 year wait, but it can be argued that the solving of the message contained within it, may have handed us two more confirmed Zodiac communications to examine, offering fresh insights into an investigation often blighted by stagnation. The Z38 can be connected to the 340 cipher through two notable portions of each code, The words IRON and DEATH can be found in both, before any period 19 shift is applied. If these two enciphered cryptograms are connected by beginning and end, then why should the middle section of the Z38 be any different. The Z38 and Z340 could very well be have a much bigger relationship, yet to be unearthed.

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

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

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

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

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

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

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

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

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

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

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

The Concerned Citizen card was mailed from San Francisco and postmarked August 10th 1969, arriving one day after the article A Murder Code is Broken which featured in the San Francisco Chronicle newspaper. In this article "Vallejo Police Sergeant John Lynch, in charge of the investigation of the murders and of the cipher letter writer, asked The Chronicle to send Harden's code breaking worksheets to him for further checking; which was done". The Concerned Citizen communication (with attached 408 cipher key) was not mailed by Donald Harden, having been sent from either a genuinely helpful citizen or from the Zodiac Killer himself. When deciding which is the case, we can look at the typed message on the card (shown below).

For somebody who pleasures in the solving of cryptograms and word puzzles, while at the same time making basic spelling mistakes and errors in punctuation, seems rather reminiscent of somebody we have become accustomed to. Three months after this correspondence, the Zodiac Killer mailed the infamous 340 cipher, a curious blend of both word puzzle and cryptogram. This cipher had "paradice" and "slaves" criss-crossed on its canvas, with a full message beneath the superficial design. The canvas and cipher both contained the encoded words of "paradice" and "slaves", thereby continuing the theme from the 408 cipher, but on this occasion he seemed eager to add a little more complexity to its design.

The decoding of the 340 cipher revealed that the majority of the message effectively ran diagonally (one down, two across) in a cipher divided up into three parts of 9, 9 and 2 rows. The last two rows were composed of a curious blend of forward and backward words, which is standard fare in the construction of word search puzzles, as is the creation of diagonal wording running across a word search grid. When we couple this with the disguised "paradice" and "slaves" running down and across the center of the 340 cipher canvas, this cryptogram becomes the embodiment of cipher and word puzzle all rolled into one.

If that wasn't enough, the Zodiac Killer would mail two more communications on December 10th 1969 and December 11th 1969 with coherent messages in the form of a pre-printed horoscope, overlayed with cryptic messages pasted predominantly 90 degrees clockwise, running down the page. These two communications were entitled Day-by-day forecast for Cancer and Day-by-day forecast for Leo. The second coming the day after the abduction of Leona LaRell Roberts (16) on December 10th 1969, leading to the possibility that this was a further play on words by the Zodiac Killer, who may have used the phrase "forecast for Leo" to insinuate the future plight of Leona Roberts. He may have had no hand in the abduction of Leona Roberts, but it wasn't unusual for the Zodiac Killer to insinuate his involvement in crimes committed by others. 

The two pasted communications in December (with Hidden and FLT a component of both) must have taken some forethought, so the idea that these two communications have no meaning whatsoever, doesn't quite sit right. These messages may need decoding just like the 340 cryptogram, albeit in a slightly different way. The choice of two horoscopes, when we consider the contemporary speculation behind the Zodiac Killer's choice of pseudonym, may have some significance. These two communications were straddled by both Fairfield letters, the first of which (December 7th 1969) contained sections of ciphertext that married up with the beginning and end of the 340 cipher. The months of July, November and December certainly seemed one big cryptic puzzle for the Zodiac Killer, but was it "one of his pleasures" in August. 

On October 22nd 1969, somebody rang the Oakland Police Department to request that either Francis Lee Bailey or Melvin Belli appear on the Jim Dunbar chat show at KGO Radio in San Francisco. Melvin Belli would co-host the morning show at approximately 6:30 am, to which, after a period of inactivity, an unknown male would call and hang up numerous times. The dysfunctional sounding caller claimed he was the infamous Zodiac Killer, a man responsible for at least five murders in the Bay Area of California.

Three people who had heard the Zodiac Killer's voice, Nancy Slover, David Slaight and Bryan Hartnell, were confident that the caller was not the man they had heard during their respective encounters with the killer. A fourth person was absolutely certain, because he was about to compose a 340 cipher denouncing the caller to the Jim Dunbar Show as a fraud, by stating "That wasn't me on the TV show". Many have found it strange that the Zodiac Killer decided to encode this denial, when he could have simply written it into the Dripping Pen card that accompanied the cipher. He clearly expected this cryptogram to be decoded fairly quickly as the message was contemporary, and of diminishing value as the years ticked by.

However, his method of encoding such contemporary information to highlight that it wasn't him on the TV show, thereby confirming that the Jim Dunbar Show caller was an imposter, was to be repeated eighteen months later. Another cryptogram would be mailed to the San Francisco Chronicle in about May of 1971, harboring a hidden message that was again contemporary in nature, while calling out an imposter. This time though, the tables would be turned. On this occasion, the Zodiac Killer would be calling out a "phony", when in realty he was the imposter and the person he was addressing was the real killer. This stemmed from his false claim that he was the murderer of Kathy Snoozy (15) and Deborah Furlong (14) in San Jose. These two young girls were brutally stabbed on August 3rd 1969 and claimed as Zodiac victims when he mailed the Dripping Pen card on November 8th 1969. He would write "Des, July, Aug, Sept, Oct = 7", thereby falsely inflating his victim count to engender more terror over a wider area.

On April 29th 1971, Karl Francis Werner was arrested for the murders of Kathy Snoozy, Deborah Furlong and Kathy Bilek, and his story was covered by Paul Avery on April 30th 1971 under the title of San Jose Student Held in Slaying of Three Girls. 
The newspaper article stated "He was immediately advised of his rights concerning any statements he may make and legal representation to which he is entitled, the detectives said. Werner was then taken to the scenes of the crimes. Late yesterday he was undergoing questioning. The detectives would not reveal what statements, if any, he had made concerning the killings of the three girls". The Zodiac Killer was understandably horrified, because the two murders he had falsely adopted into his victim total for a year-and-a-half, were about to be handed over to someone else. Karl Francis Werner was ultimately charged (and later convicted) of all three murders, but the Zodiac Killer was having none of it, firing off a 148 character cipher and letter sometime in May (see below).

Just like his encoded message in the 340 cipher stating "That wasn't me on the TV show", he would again encode the following message "Tis the Zodiac Speacking. Why can't you stop me. I can't stop killing. Stop listening t(o) phonys. If this is not on your front page in a week I will skin 3 little kids and make a suit from the skin". The Zodiac Killer was responding to the Paul Avery newspaper article, informing everybody that they should pay no attention to Karl Francis Werner and insisted they should "Stop listening to phonys". One can't help seeing the irony of the situation. The Zodiac Killer effectively declared that the caller to the Jim Dunbar Show was a phony because it wasn't him on the TV show, but has now become the phony calling out the real killer - and both of these declarations hidden within cryptograms separated by eighteen months. The Zodiac Killer felt angered enough to dissuade law enforcement in listening to Karl Francis Werner, yet disguised this pertinent message behind a wall of coding, just as he had done on November 8th 1969 with another contemporary message. However, there was one big difference. This latest cryptogram had returned back to the standard left-to-right homophonic technique employed by the 408 cipher. Bearing in mind his 340 cipher was yet to be deciphered - and knowing he wanted to declare Karl Francis Werner a fraud while it still mattered - the Zodiac Killer probably thought it wise to return back to the simplest form of encryption.

Early in December 2020, the 340 cipher was cracked by David Oranchak, Sam Blake and Jarl Van Eycke, which revealed the message shown below. Despite the fact the message left many rather deflated because of its banality, hoping it would reveal so much more, the message contained in the Dripping Pen card and the following Fairfield letters appear to show a running theme. It was recently highlighted how the 38 character code in the December 7th 1969 communication (1st Fairfield letter) showed a distinct correlation to the 340 cipher. Here is a brief recap:

If a Zodiac impersonator had created the 38 character code, this hoaxer would have had to guess that by separating the prominent ZO∆AIKꞮ+ characters on the bottom line of the 340 cipher, into AIKꞮ+ on the bottom line of the 38 character code, he would be reducing these characters to create something meaningful. He apparently did. By separating these characters into the five visible at the end of the 38 character code, he created the word "death", just like the solved 340 cipher. Druzer, an excellent Zodiac researcher, pointed out the same thing, stating "The most curious/compelling feats are that the author isolated actual words, most notably death, and that he refrained from copying Zodaik, which would certainly be expected of a hoaxer". In other words, he dismantled the ZO∆AIK element, while leaving Ɪ+ in place, to form "death" as the final word on the 38 character code. This appears to show knowledge of the hidden message in the 340 cipher. But there is so much more in the Fairfield letters that harks back to the Dripping Pen card and 340 cipher.

Despite stating in the above message he now had enough slaves to work for him in paradice, he would ultimately decide to "kill again" on December 7th 1969, in accompaniment to his brief 38 character code. The Zodiac Killer would never use the standalone word "life" outside of the November 8th and December 16th communications, yet he would end the 340 message with "life will be an easy one in paradice [death]", and begin the December 16th 1969 communication (2nd Fairfield letter) with "I just need to tell you this state is in troulbe, I will go for the Goverment life".

The Dripping Pen card containing the 340 cipher stated "Could you print this new cipher in your frunt page?", whereas the wording "you better print" preceded the small 5/9 character code in the December 16th 1969 letter. The decoded message in the 340 cipher (unknown to anyone until December 2020) began in mocking fashion, stating "I hope you are having lots of fun trying to catch me", while the message immediately beneath the small code in the December 16th 1969 letter stated "you will not catch me". It was almost as though the Zodiac Killer was replying to himself just over five weeks later, in absence of his cipher being solved.

On October 22nd 1969, the Oakland Police Department took a call in the early morning hours from somebody claiming to be the Zodiac, requesting that either Melvin Belli or Francis Lee Bailey, high profile lawyers at the time, appear on a chat show hosted by Jim Dunbar later that day. Melvin Belli agreed to appear on the show to which a man would eventually contact via telephone, claiming not only his name was 'Sam', but also by inference that he was the infamous Zodiac Killer. It was very quickly determined from Nancy Slover, David Slaight and Bryan Hartnell that the caller to the TV show wasn't the Zodiac Killer, which was confirmed by the decoded 340 message, which read "That wasn't me on the TV show". However, the Zodiac Killer didn't expand on who the person was that made the phone call to the Oakland Police Department. Whether he was leaving this open to speculation deliberately, nobody knows, but Oakland would feature in his murder destinations on December 16th 1969. This was the only time this city would feature by way of written text in any of the Zodiac Killer's communications, and it came just five weeks after the Bay Area murderer encoded the denial of "That wasn't me on the TV show". Was it a subtle admission that he did make the Oakland phone call to police and was now promising to murder eight of them, hence the renewed contact with Melvin Belli just four days later providing a piece of Paul Stine's shirt?

There are three things a hoaxer should not have known regarding the decoded 340 cipher message. [1] He shouldn't have known that by separating ZO∆AIKꞮ+ into AIKꞮ+ that it would produce the word "death" at the end of both codes, and provide a common link between the two. [2] He shouldn't have known that the opening line of the 340 message read "I hope you are having lots of fun trying to catch me", when he replied "you will not catch me" only 38 days later, unless you maintain that this is a coincidence. [3] He shouldn't have known that the Oakland inspired TV show had featured as a denial by the Zodiac Killer in the message, when he listed Oakland in the list of his murder sites.

The word "death" could be decoded using the Zodiac key through both the Z340 and Z38 within 29 days of one another. The December 16th 1969 letter also contained a configuration of four smaller crosshairs positioned around larger crosshairs, similar to the configuration of By Knife, By Gun, By Rope and By Fire on the Halloween card mailed on October 27th 1970. However, on this occasion the design was preceded by five characters. Could this be the word "death" once again, mirroring the Tim Holt comic book which likely inspired the design of the Halloween card in the first place? Anyway, "I thought you would nead a good laugh before you hear the bad news. Ha! Ha! Ha!"   

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

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

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

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

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

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

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

Here is the message in the 340 character cipher (corrected for spelling mistakes), split into three sections of nine, nine and two rows. The message in the first two sections has been left untouched, while in the third section only one word has been shifted.

The word "DEATH" has been moved from the end of the original message to the beginning of the nineteenth line. It now reads:

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 DEATH. LIFE WILL BE AN EASY ONE IN PARADICE.

Since the decoding of the Zodiac Killer's infamous 340 cipher by Dave Oranchak, Sam Blake and Jarl Van Eycke earlier this month, it is now possible to almost certainly confirm the two letters mailed on December 7th 1969 and December 16th 1969 as authentic Zodiac communications. It has long been known that these two letters were authored by the same person, but it has always been difficult to convince certain sections of the Zodiac community these letters were penned by the Zodiac Killer, who insisted they were a hoaxer based on nothing more than handwriting analysis and the disorganized appearance of the coding in each. The following, will hopefully show that handwriting alone should never be used to dismiss a questioned Zodiac correspondence. By examining the encryption methods between the 340 and 38 character codes, much can be revealed

A 38 character code accompanied the Fairfield letter on December 7th 1969, just twenty-nine days after the Zodiac Killer's recently deciphered 340 cipher. This code contained only characters available in the 340 cipher, unlike the following 13-Symbol and 32-Symbol ciphers. This opened the door to the possibility that the 38 character code was somehow related to the 340 cipher and maybe contained a clue to its construction. Druzer, an avid and diligent Zodiac researcher, mailed me the 38 character code deciphered with the 340 cipher key. The result is mostly garbled, but he drew my attention to the final line of both codes ending in "death". The Zodiac Killer only took a 4+ horizontal combination of characters from the 340 cipher to the 38 character code on two occasions. Those were HER> and AIKꞮ+, which spelled the standalone words of IRON and DEATH, before the diagonal shift was applied to the 340 cipher to reveal the message. Despite the last two rows of the 340 cipher being a mixture of forward and backward reading words, the word "death" sits at the end of both the 340 and 38 character ciphers, indicating that this word likely concludes the message of the rearranged final two lines. It could mean that the final sentence of the 340 cipher is "life is death" rather than "death is life".   

Other horizontal words do exist in this format, however, the Zodiac Killer gave us 4 and 5 characters which bound the 340 and 38 character ciphers together, and both formed English words. The Zodiac Killer began and ended his 38 character code with two prominent sections from the start and end of the 340 cipher, both of which contained visible words before any shift was applied (The final word remaining static). This may be another observation, which confirms to the doubters the December 7th 1969 letter as an authentic Zodiac communication. Unless of course, the 38 code hoaxer identified two passages of 4 and 5 characters from the undeciphered 340 cipher, that just happened to accidentally find two English words after the 340 key was applied, specifically the two which began and ended the 340 cipher. This hoaxer would also have to guess that by separating the prominent ZO∆AIKꞮ+ characters on the bottom line of the 340 cipher, into AIKꞮ+ on the bottom line of the 38 character code, he would be reducing these characters to create something meaningful. He apparently did. By separating these characters into the five visible at the end of the 38 character code, he created the word "death", just like the solved 340 cipher. Druzer pointed out the same thing, stating  "The most curious/compelling feats are that the author isolated actual words, most notably death, and that he refrained from copying Zodaik, which would certainly be expected of a hoaxer". In other words, he dismantled the ZO∆AIK element, while leaving Ɪ+ in place, to form "death" as the final word on the 38 character code. This appears to show knowledge of the hidden message in the 340 cipher

This also opens up the possibility that the word "death" was present in the 5 character code on December 16th 1969, when the Zodiac Killer mailed his second Fairfield letter mimicking the yet to be designed Halloween card. The word "death" would then span three consecutive Zodiac ciphers from November 8th 1969 to December 16th 1969, with the Halloween card on October 27th 1970 the icing on the cake.

The November 8th 1969 greeting card came without a section of Paul Stine's shirt, as did the two Fairfield letters on December 7th 1969 and December 16th 1969. When neither of the Fairfield letters were published in the newspapers, the Zodiac Killer would add a shirt piece to the Melvin Belli letter just four days later. In the Melvin Belli letter the Zodiac Killer pleaded for help on four occasions, stating "please help me" on three of those occasions. The unpublished December 7th 1969 letter contained the phrase "I just need help".

In the early morning hours of October 22nd 1969, somebody claiming to be the Zodiac Killer called the Oakland Police Department and requested that Francis Lee Bailey or Melvin Mouron Belli appear on the Jim Dunbar Show at KGO Radio in San Francisco, to which he would ring in. Somebody did ring the chat show, but this caller was later identified as mental patient, Eric Weill. However, we still don't know to this day whether the original caller to the Oakland Police Department was the Zodiac Killer or not, because the genuine Zodiac Killer only stated "That wasn't me on the TV show" in his now decrypted 340 cipher. At no point did he deny being the caller to the Oakland Police Department.

Probably the most important question to ask, is why would the Zodiac Killer choose to ring the Oakland Police Department above any other. There appeared no connection between the Zodiac Killer and Oakland prior to October 22nd 1969. However, this was also the case on October 15th 1969, when the Zodiac Killer almost certainly phoned the Santa Rosa Police Department to threaten schoolchildren on buses, who then implemented the routine checking of every school bus for hidden bombs. This caller, claiming to be the Zodiac Killer, was threatening schoolchildren two days before the details of "School children make nice targets, I think I shall wipe out a school bus some morning" was released into the newspapers.

On October 21st 1969, the day before the Oakland Police Department call, somebody claiming to be the Zodiac Killer rang the Palo Alto Times newspaper. The Palo Alto Times reported on October 22nd 1969, that Patrol cars convoyed school buses around Palo Alto yesterday after a telephoned murder threat by a man claiming to be the Zodiac killer of five persons. The caller to the Palo Alto Times said he intended to "pick the kids off as they get on the school bus". The weird slayer, who signs himself "The Zodiac", made a similar threat in a letter to the San Francisco Chronicle last week after the Oct. 11 shooting of a taxi driver. This would come only six days after the Santa Rosa threat on schoolchildren. The caller also stated to the Palo Alto Times that he had left San Francisco "because I'm too hot there". On December 8th 1969, somebody claiming to be the Zodiac Killer rang commercial radio station KTOK in Oklahoma City, claiming he left California "because it got too hot for me". There was a further call on December 19th 1969, the day before the Melvin Belli letter, threatening "I am going to kill five of you officers and a family of five between now and Monday". This call was received by Shirley Searey, a police dispatcher at the San Jose Highway Patrol.

Captain Martin Lee stated, after the Zodiac Killer's October 13th 1969 letter: "His boast of being in the area we were searching was a lie. We had the whole area flooded with lights. We had seven police dogs and a large number of patrolmen searching the area tree by tree and bush by bush. The dogs are the best in the country". Captain Lee added that Zodiac's failure to mention the dogs and floodlights was proof "he wasn't anywhere in the vicinity". The Zodiac Killer responded on November 9th 1969 with "I have grown rather angry with the police for their telling lies about me. The dogs never came with in 2 blocks of me + they were to the west + there was only 2 groups of parking about 10 min apart then the motor cicles went by about 150 ft away going from south to north west".

However, this ire likely began on October 15th 1969, when the San Francisco Chronicle failed to publish his threat on schoolchildren, resulting in his phone call to the Santa Rosa Police Department. The call to Oakland Police Department on October 22nd 1969 may have been triggered by these perceived slights from law enforcement. By avoiding the San Francisco Police Department and calling the Oakland Police Department on October 22nd 1969, the Zodiac Killer could request a prominent attorney to represent him on the Jim Dunbar Show, and set the record straight on the misinformation and lies spoken about him by Captain Martin Lee to the San Francisco Chronicle. This TV audience on the popular Jim Dunbar Show in San Francisco may have been the ideal way to set the record straight, circumventing the San Francisco Police Department and San Francisco Chronicle and receiving maximum exposure. Ultimately, the Zodiac Killer may have had second thoughts, surmising that it could have led to somebody identifying him. This hesitancy opened the door to hoaxer Eric Weill.

Despite the phone call to the Jim Dunbar Show having been roundly dismissed as the Zodiac Killer "by three who knew", the murderer of five still felt compelled to disassociate himself from being the caller to the TV show, by mailing a cryptogram and greeting card on November 8th 1969. If the Zodiac Killer had rang the Oakland Police Department on October 22nd 1969 with the intention of appearing on the Jim Dunbar TV show and setting the record straight concerning Captain Martin Lee and the San Francisco Police Department - then having not done so - one would have expected his next communication to do exactly that. Therefore, it's no surprise that the Bus Bomb letter on November 9th 1969 was the Zodiac Killer's longest communication of them all, attacking the police with the venom he so wanted to do with a captive TV audience. The two communications on November 8th 1969 and November 9th 1969, inextricably bound by his failure to appear on the Jim Dunbar Show just over two weeks earlier.

The phone calls wouldn't stop there, when Daniel Williams (24), a Salesian High School teacher, started to receive malicious phone calls to his 1234 Bush Street, Martinez residence on October 23rd 1969. These calls continued for ten days and culminated with somebody breaking into his residence on November 2nd 1969 and lacing his 7-Up soft drink with enough arsenic to kill. The caller, claiming to be the Zodiac Killer, told Daniel Williams over the phone that he "had gone to a Martinez school in search of victims but left when he found police there", mocking law enforcement by stating “I’m too smart for them". This was considered particularly relevant because of the language Zodiac adopted on November 9th 1969 in the Bus Bomb letter mailed to the San Francisco Chronicle of "The police shall never catch me, because I have been too clever for them".

On Wednesday, November 5th 1969, somebody rang the Martinez Police Department at 12:30 am stating "There's going to be a shooting at 1234 Bush Street", before immediately hanging up. The threat to find victims at a Martinez school, coupled with the menacing phone calls, were not dissimilar to recent Zodiac activity during the month of October. After the threat to shoot Daniel Williams at his residence, police instigated surveillance in the immediate area of Bush Street for the remainder of that morning, but no suspicious activity was detected. The next Zodiac Killer communications would be postmarked just two and three days later, with the promise of more bad news and a victim count left dangling at the end of October. If the perpetrator of the crimes inflicted upon Daniel Williams wasn't the Zodiac Killer, then it was a pretty determined hoaxer claiming to be him. The call to Oakland Police Department was made on October 22nd 1969, with the threats on Daniel Williams beginning just a day later, on October 23rd 1969. The Salesian High School where Daniel Williams worked, only thirteen miles north of the Oakland Police Department. When we place all of this in context, does it indicate that the Zodiac Killer was likely the caller to Oakland Police Department on October 22nd 1969, or did Eric Weill just spontaneously call law enforcement because he had nothing better to do at the time? 

There is an extremely interesting thread on the Zodiac Killer Site forum, initiated by Paul_Averly under the title The 340 is a Skytale Cipher. He begins "Major Congrats to doranchak! If anyone could do it, he and his team were definitely the ones! I too have something to contribute to this major breakthrough". Please take a read.

The Skytale Cipher technique involves rolling a band around a rod, to which a message is applied. When the band is unrolled the message is scrambled in ciphertext form. Only by re-wrapping the band around a same sized rod will the message reappear. I have followed the thread and the technique appears to work on the text of the 340 cipher as shown here. The thread ponders the question of where did the Zodiac Killer get his inspiration for the design of the 340 cipher, that baffled investigators for fifty-one years until Dave Oranchak, Sam Blake and Jarl Van Eycke cracked the cipher on December 3rd 2020. 

There is a strong possibility the answer lies in the October 22nd 1969 San Francisco Examiner newspaper article by Will Stevens, entitled Cipher Expert Dares Zodiac to Tell Name, in which Dr. D.C.B Marsh laid down a challenge to the Zodiac Killer. The newspaper stated Dr Marsh told the Examiner today: "The killer wouldn't dare, as he claimed in letters to the newspapers, to reveal his name in the cipher to established cryptogram experts. He knows, to quote Edgar Allan Poe, that any cipher created by man can be solved by man. Zodiac has not told the truth in his cipher messages to the Examiner, the Chronicle and the Vallejo Times-Herald. Zodiac has not done this, because to tell the complete truth in relation to his name - in cipher code - would lead to his capture. I invite Zodiac to send The American Cryptogram Association a cipher code - however complicated - which will truly and honestly include his name".

The key line the Zodiac Killer may have picked up on was "He knows, to quote Edgar Allan Poe, that any cipher created by man can be solved by man". So, where would the Zodiac Killer go to design a cipher? He would go to Edgar Allan Poe and create a cipher described at length in one of Poe's well known Essays. This is the first section of Edgar Allan Poe's A Few Words on Secret Writing:

As we can scarcely imagine a time when there did not exist a necessity, or at least a desire, of transmitting information from one individual to another, in such manner as to elude general comprehension; so we may well suppose the practice of writing in cipher to be of great antiquity. De La Guilletiere, therefore, who, in his “Lacedaemon Ancient and Modern,” maintains that the Spartans were the inventors of Cryptography, is obviously in error. He speaks of the scytala as being the origin of the art; but he should only have cited it as one of its earliest instances, so far as our records extend. The scytalae were two wooden Cylinders, precisely similar in all respects. The general of an army, in going upon any expedition, received from the ephori one of these cylinders, while the other remained in their possession. If either party had occasion to communicate with the other, a narrow strip of parchment was so wrapped around the scytala that the edges of the skin fitted accurately each to each. The writing was then inscribed longitudinally, and the epistle unrolled and dispatched. If, by mischance, the messenger was intercepted, the letter proved unintelligible to his captors. If he reached his destination safely, however, the party addressed had only to involve the second Winder in the strip to decipher the inscription. The transmission to our own times of this obvious mode of cryptography is due, probably, to the historical uses of the scytala, rather than to anything else. Similar means of secret intercommunication must have existed almost contemporaneously with the invention of letters.

It may be as well to remark, in passing, that in none of the treatises on the subject of this paper which have fallen under our cognizance, have we observed any suggestion of a method — other than those which apply alike to all ciphers — for the solution of the cipher by scytala. We read of instances, indeed, in which the intercepted parchments were deciphered; but we are not informed that this was ever done except accidentally. Yet a solution might be obtained with absolute certainty in this manner. The strip of skin being intercepted, let there be prepared a cone of great length comparatively–say six feet long–and whose circumference at base shall at least equal the length of the strip. Let this latter be rolled upon the cone near the base, edge to edge, as above described; then, still keeping edge to edge, and maintaining the parchment close upon the cone, let it be gradually slipped towards the apex. In this process, some of those words, syllables, or letters, whose connection is intended, will be sure to come together at that point of the cone where its diameter equals that of the scytala upon which the cipher was written. And as, in passing up the cone to its apex, all possible diameters are passed over, there is no chance of a failure. The circumference of the scytala being thus ascertained, a similar one can be made, and the cipher applied to it.

The Zodiac Killer reads this article and adopts the very technique described by Edgar Allan Poe, an author and cryptographer mentioned by Dr. D.C.B Marsh. But this isn't all. Where did the inspiration for the Zodiac Killer's third cipher come from? 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. I will let you unravel the rest. Here is the relevant passage:

"Were two individuals, totally unpractised in cryptography, desirous of holding by letter a correspondence which should be unintelligible to all but themselves, it is most probable that they would at once think of a peculiar alphabet, to which each should have a key. At first it would, perhaps, be arranged that a should stand for z, b for y, c for x, d for w, &c. &c.; that is to say, the order of the letters would be reversed. Upon second thoughts, this arrangement appearing too obvious, a more complex mode would be adopted. The first thirteen letters might be written beneath the last thirteen, thus:
n o p q r s t u v w x y z
a b c d e f g h i j k I m; and, so placed, a might stand for n and n for a, o for b and b for a, &c. &c. This, again, having an air of regularity which might be fathomed, the key alphabet might be constructed absolutely at random".

Again, the following section of A Few Words on Secret Writing details a shifting alphabet using two concentric circles, where the outer circle and inner circle have a common center. Using the alphabet and your message, it is possible to encode your message while turning the outer circle a set number of places between each encryption to increase difficulty. Here is the excerpt from the Essay:

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

This is extremely pertinent when we consider the design of the 13-Symbol cipher on April 20th 1970. It contains three circled eights, all the components of which are present on the Union Cipher Disk. This cipher disk employs the same technique described by Edgar Allan Poe above, but more importantly it contains the numbers 000 and 888 on its face, exactly the same as Zodiac added to his 13-Symbol cipher. Was the Zodiac Killer hinting that the concentric circle had to be rotated at these particular points during encipherment?

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

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

If the Zodiac Killer was inspired to seek out Edgar Allan Poe by the words of Dr. D.C.B Marsh in the San Francisco Examiner on October 22nd 1969, then the A Few Words on Secret Writing had all the components required for his second and third ciphers. It had the Skytale Cipher (shown by Paul_Averly to work on the 340 cipher), followed by Poe's description of splitting the alphabet into two parts of thirteen (one beginning with A and ending with M just like the 13-Symbol cipher), and finally, the description of two concentric circles to encode a message, just like the Union Cipher Disk that contained 000 and 888.