Zodiac Killer – Z340 Cipher Cracked After 50 Years

By: Dr Tristan Jenkinson

Introduction

It was announced yesterday (11 December 2020) that a group of three code-breakers have successfully decrypted one of the ciphers (known as Z340) written by the Zodiac killer back in 1969.

I have a background in mathematics and an interest in puzzles and have spent some time looking at the Zodiac ciphers previously, including working through information on David Oranchak’s website Zodiac Killer Ciphers – Can you help solve the codes? and his online system to investigate the Z340 cipher. David Oranchak is one of the three experts who made the breakthrough this week.

The Zodiac Killer

The Zodiac Killer was a serial killer known to be active in San Francisco in the late 1960’s and early 1970’s. Though police tied five deaths to the killer, he claimed to have killed thirty seven. He has yet to be identified, though there has been much speculation as to his potential identity. There have been thousands of suspects since the late 1960s. For example “The Most Dangerous Animal of All” documentary which aired earlier this year in the US, in which Gary Stewart alleges that his father was the infamous serial killer and Xenophon Anthony (who was allegedly identified by an 8 year old eye witness to one of the murders).

The Zodiac killer has been the subject of many web based discussions, documentaries and a film by David Fincher. His ciphers have captured the attention of many – and appear to have been an unlikely form of inspiration for an unusual McDonalds ad campaign.

Perhaps one reason that the Zodiac killer has retained such notoriety is that he sent a series a letters and ciphers to police and newspapers, making threats and talking about what he had done. The ciphers have been a source of great interest to code breakers for many years. The Cipher known as Z340 (recognised by code breakers to be one of the most difficult codes to break) has been a mystery for over 50 years.

The Ciphers

The Zodiac killer sent a series of four ciphers in total, they are generally referred to by the letter Z and the length of the code provided.

  • Z408 (July 1969) – This was the first cipher sent by Zodiac. It was actually split into three sections and mailed to separate newspapers in San Francisco. Zodiac threatened to go on a “kill rampage” if they were not printed. The newspapers decided to publish the cipher and it was cracked by a husband and wife (Donald and Bettye Harden) within days. The cipher was relatively simple, with direct substitutions for symbols and letters (though some letters were represented by more than one symbol).
  • Z340 (November 1969) – This is the cipher that has just been cracked. It was sent directly to the San Francisco Chronicle, who also broke the news of the cipher being broken this week.
  • Z13 (April 1970) – A very short cipher which followed the text “My name is – “. There are many doubts that the cipher would actually reveal the identity of the Zodiac killer. It is so short (just 13 characters that finding and verifying any result would be virtually impossible without further information.
  • Z32 also known as the “map code” (June 1970). This cipher was sent to the San Francisco Chronicle, together with a map and the text “The map coupled with this code will tell you where the bomb is set. You have untill [sic.] next Fall [sic.] to dig it up.” Though several people have claimed to provide full or partial solutions, no confirmed solution has ever been found.

Previous Attempts

There have been many previous attempts and claimed solutions to Z340. The most widely considered of these was an alleged partial solution by Craig Bauer which formed part of a documentary “The Hunt For The Zodiac Killer”. You can read more about here. While Bauer’s approach provided some potentially meaningful text, such as “I KILL BOTH NIGHT AND DAY” and “I LIVE BY THE GUN”, significant doubts were raised with the solution. Given the new breakthrough, this partial solution is confirmed as being incorrect.

The Solution

David Oranchak, Sam Blake and Jarl Van Ecke are credited with the breakthrough, and their solution has been confirmed by the FBI, who said in a statement released on Twitter “The FBI is aware that a cipher attributed to the Zodiac Killer was recently solved by private citizens”. The FBI have been reported as also stating “On December 5, 2020, the FBI received the solution to a cipher popularly known as Z340 from a cryptologic researcher and independently verified the decryption”.

The solution provided by Oranchak and the team 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 WILL BE AN EASY ONE IN PARADICE DEATH

The cipher was actually split up into several pieces and the text has to be read in a specific order – meaning that to decipher it, you have to know not only know the substitution rules (for letters and symbols) but also the order in which the symbols need to be read.

David Oranchak has released a video update in the latest episode of his series “Lets Crack Zodiac”. David’s video provides significant details of the method used to solve the Z340 cipher. You can view it here.

The approach involved the using a computer program to create 65,000 different versions of the encrypted text (each organising the ciphertext in a different order), then using a decryption tool (AZ Decrypt – written by Jarl Van Ecke) to try and decrypt each of the 65,000 versions.

One of the solutions stood out, apparently containing the text “HOPE YOU ARE TRYING TO CATCH ME” and “OR THE GAS CHAMBER”. The team investigated this solution to see the structure of how it was build, and then further refined the approach.

It was found that the cipher was in three sections, two of which were 9 lines long, and a final section of just two lines. A diagonal pattern was used for the ordering of the text. There also appear to have been errors made by Zodiac, which the team have identified and proposed solutions to.

“That Wasn’t Me”

The solution contains references which are relevant. There is a statement that “THAT WASNT ME ON THE TV” as well as references to the “GAS CHAMBER”. The Z340 cipher was sent to the San Francisco Chronicle around two weeks after somebody claiming to be Zodiac (who used the name “Sam”), dialed into a TV show hosted by Jim Dunbar and Melvin Belli, who specifically mention the gas chamber – see more details about the show here – http://zodiackillerfacts.com/myths-legends/melvin-belli-the-zodiac-birthday-call/. It was generally accepted that “Sam” was not the Zodiac killer.

Conclusion

A 50 year old puzzle has been solved. While the solution is a great achievement and puts to bed many years of speculation, sadly it does not provide much more information on the killer himself and his identify remains uncovered. The FBI continue their investigation.

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