The infamous serial killer murdered at least five people in northern California, U.S, during 1968 and 1969.
The Zodiac was never caught despite sending a series of taunting letters and word puzzles to San Francisco newspapers up until 1974.
Some were accompanied by bloodied fragments of clothing as proof.
The Zodiac’s infamous 340 Cipher sent to the San Francisco Chronicle in 1969, accompanied by the ‘Dripping Pen card’
One of the four ciphers was solved in 1969, in which the Zodiac said he was killing people to collect as slaves for the afterlife.
The remaining three cryptograms have captivated amateur sleuths for more than 50 years in the hope that solving them may lead to the identity of the killer.
Melbourne mathematician Samuel Blake along with two other code breakers from the U.S and Belgium have now cracked the 340 Cipher, a 340-character puzzle sent by the serial killer to the San Francisco Chronicle on November 8, 1969.
The shocking fragment that led to them cracking the code were the chilling words ‘GAS CHAMBER’, he said.
Dr Blake got interested in the Zodiac’s riddles after seeing online videos from U.S. cryptologist David Oranchak who has been trying to crack the code for 15 years.
‘It was sort of a way to get through the Melbourne covid lockdown, was to play around with this in my spare time,’ Dr Blake told ABC News on Saturday.
Dr Blake, a visiting fellow at the University of Melbourne, reached out to Mr Oranchak in March then worked on decoding the message using the university’s supercomputer Spartan.
Melbourne mathematician Samuel Blake used the University of Melbourne’s supercomputer Spartan to run 650,000 variants of the code until the key words ‘GAS CHAMBER’ popped out
Belgian programmer Jarl Van Eycke (left) designed the software that helped solve the riddle. US code-breaker David Oranchak (right) worked for 15 years to crack Cipher 340
The team tried 650,000 different ways to solve the cypher.
‘Just by chance we happened to stumble upon a fragment of how it could be solved,’ he said.
The macabre fragment that popped up in the sea of noise was ‘GAS CHAMBER’.
‘Using that fragment we were able to reverse engineer the entire solution, and got the entire message out from the Zodiac,’ he said.
The Zodiac’s riddle was a homophonic substitution cipher, where large areas of text was replaced with symbols.
Dr Blake said the Zodiac’s trick that made it so hard to solve was that it was not written left-to-right and top-to-bottom as English text is normally read.
A police sketch of the San Francisco Zodiac Killer, who has never been identified
Three of the known victims of the Zodiac Killer. L-R: Betty Lou Jensen, David Faraday and Darlene Ferrin. The Zodiac claimed to have killed up to 37 people but only five are confirmed
Instead, the reading direction went down the diagonals of the page, from one row down and two columns across, to the next row down, two columns across.
‘Trying to stumble across that correct enumeration was one of the main difficulties,’ he said.
Dr Blake paid tribute to both Mr Oranchak and Belgium-based software programmer Jarl van Eycke whose software program, azdecrypt helped the team crack the code.
While the message does not reveal the killer’s identity, it may give a clue to help the authorities identify him.
FULL TEXT OF ZODIAC KILLER’S 340 CIPHER
The full text of the decrypted 340 Cipher reads as follows:
‘I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME THAT WASNT 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’
The message was sent all in capital letters, without punctuation and included the misspelling of ‘paradise’.
The TV show the message refers to was The Jim Dunbar Show, a Bay Area television talk show at the time, CNN reported.
A person claiming to be the Zodiac Killer had called into the show two weeks before the cipher was sent.
Dr Blake also said his team of amateur code-breakers was looking to see whether their work on solving the 340 Cipher could help solve the remaining two Zodiac cryptograms.
One reads ‘My name is ____’ followed by 13-character cipher.
The other, called Z32, was a 32-character cryptogram also known as the ‘map code’ as it was part of a letter warning of a buried bomb, accompanied by a map.
Boastful letters from the Zodiac claiming he had killed seven people
The Zodiac’s 13-character cipher (pictured left) hasn’t been cracked but Dr Blake said he and his team are now looking at it. Pictured: San Francisco police wanted bulletin, Zodiac letters
The Zodiac case is still open and cold-case detectives from the San Francisco FBI and San Francisco Police Department are now looking at the new evidence
The Zodiac claimed he had killed as many as 37 people.
The FBI said in a statement on Saturday that the case remains an ongoing investigation.
‘The Zodiac Killer terrorized multiple communities across Northern California and even though decades have gone by, we continue to seek justice for the victims of these brutal crimes,’ the FBI San Francisco said on Twitter.
Both the FBI and the San Francisco Police Department are looking at the solved cipher which has been sent to cold case homicide investigators.