The Zodiac Killer’s Infamous Z340 Cipher Has Been Solved More Than 50 Years After His Chilling Murders Took Place

First sent to The San Francisco Chronicle by the Zodiac Killer on November 8, 1969, the Z340 cipher proved utterly baffling — until now.

FBIThe Zodiac Killer’s cipher known as Z340, now finally solved after more than a half-century.

In April 2024, an international team of cryptographers published a whitepaper detailing the extensive process of decoding the Zodiac Killer’s Z340 cipher. The process involved a massive amount of work, crowdsourcing, and computational programming, and though this process was first detailed in a 2020 YouTube video, the new whitepaper is the most comprehensive overview of how it was done.

Three men — David Oranchak, Sam Blake, and Jarl Van Eycke — are primarily responsible for solving the Zodiac Killer’s cipher, but in their paper they make it clear that this would not have been possible without significant contributions from many others over the years.

This is the story of the Zodiac Killer cipher known as Z340, how it was solved, and what it says.

Who Was The Zodiac Killer And What Did He Do?

Public DomainA wanted poster for the Zodiac Killer, featuring a composite sketch of his purported appearance.

The Zodiac Killer was an unidentified serial killer who operated in Northern California in the late 1960s and perhaps early 1970s. The Zodiac is infamous not only for a series of brutal murders, but also for taunting police and the public with cryptic letters, ciphers, and phone calls.

The Zodiac Killer claimed responsibility for at least five murders between 1968 and 1969, targeting several young couples and one lone male cab driver. His known victims were David Faraday, Betty Lou Jensen, Darlene Ferrin, Michael Mageau (survived), Bryan Hartnell (also survived), Cecelia Shepard, and Paul Stine.

The Zodiac Killer’s letters, which were sent to local newspapers, included detailed descriptions of the crimes, and he demanded they be published. Some of these letters contained complex cryptograms, which remained unsolved for more than half a century, though some of these Zodiac ciphers have allegedly been solved in recent years.

Despite extensive investigations, the Zodiac Killer was never caught and his identity remains a mystery. Over the years, numerous sleuths have claimed to solve the Zodiac case, with suspects like Gary Francis Poste and Arthur Leigh Allen among the most prominent, but none of these men have been definitively proven to be the Zodiac.

The case has fascinated the public and investigators for decades, spawning numerous books, movies, and theories about the killer’s identity.

How Cryptographers Decoded The Zodiac Killer’s Cipher Known As Z340

David Oranchak, Sam Blake, and Jarl Van EyckeA breakdown of the various characters used in the Z340 Zodiac Killer cipher.

The Zodiac Killer’s second cipher, known as the Z340 letter, was sent to The San Francisco Chronicle on November 8, 1969, and proved to be astonishingly difficult to decode. It was so difficult, in fact, that it took 51 years before anyone was able to crack it.

That day came on December 5, 2020, when U.S.-based software developer David Oranchak, Australian mathematician Sam Blake, and Belgian cipher expert Jarl Van Eycke uncovered the mystery behind the Zodiac Killer’s cipher and had their work confirmed by the FBI. Earlier this year, the three men published a whitepaper detailing their extensive process, showing just how much work was necessary to decipher the letter.

They found that Z340’s cipher alphabet consisted of 63 different symbols — a system complicated even further because multiple symbols could each represent a single letter from the alphabet. Moreover, the letter was rife with misspellings and transpositions, which made the codebreaking all the more complex.

However, software created by Van Eycke called AZdecrypt finally helped reveal the solution, which the authors said would not have been possible if not for “hundreds, if not thousands” of purported solutions offered by others over the years.

“Shortly after Zodiac mailed [Z340], many people raced to decipher it, and some asserted their decryptions were correct,” they wrote. “But none were definitively endorsed by law enforcement, so these efforts continued for decades.”

The report also outlined just how many attempts were made over the years to crack the code. The FBI failed to do it, as did the NSA and the Navy. The American Cryptogram Association also made attempts over the years, but none of them were able to conclusively decipher it.

“The popularity of the case and noteworthy nature of Z340 led many amateur codebreakers to join the efforts to solve the cipher,” the three cryptographers wrote. “Many so-called solutions were developed that ‘went viral’ and received significant attention in the news media.”

FBIAn excerpt of the Zodiac Killer’s Z340 cipher, including his infamous crosshairs signature.

But it was a new update to Van Eycke’s AZdecrypt that finally helped to crack the code.

Since Z340 and another cipher, Z408, lack divisions between words, any software that had previously attempted to decipher it also lacked those divisions. The result was often a jumbled mess, since words blurred together and the complex nature of the cipher meant one couldn’t be quite sure if the letters themselves were even accurate.

AZdecrypt, however, could now automatically add white spaces to divide words where they likely belonged, based on a wealth of statistics.

“This made partial solutions much more comprehensible,” the authors said.

So now, more than 50 years after the Zodiac Killer sent Z340, we finally know what it says.

The Decoded Text Of The Zodiac Killer’s Z340 Cipher

“I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME,” the Z340 cipher begins. “THAT WASN’T ME ON THE TV SHOW” — referring to a recent live call-in purportedly from the Zodiac on A.M. San Francisco. The cipher continues:

“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”

While this deciphered message doesn’t solve all of the mysteries surrounding the Zodiac Killer, it is still a remarkable feat. Oranchak, Blake, and Van Eycke certainly deserve credit for revealing the letter’s contents to the world, but the cryptographers also made it clear that their work would not have been possible without those who came before them.

“The solution of this cipher was the result of a large, multi-decade group effort,” they wrote, “and we ultimately stood on the shoulders of many others’ excellent cryptanalytic contributions.”

Perhaps future sleuths will in turn build upon these efforts to shed further light on the story of the Zodiac Killer.

After reading about how the Zodiac Killer cipher Z340 was finally solved, learn all about the most intriguing Zodiac Killer suspects. Then, read about Paul Avery, the journalist targeted by the Zodiac Killer.