Stephen Ornes

In the late 1960s, a serial killer self-identifying as “the Zodiac” killed at least five people in Northern California and claimed to have murdered more. In November 1969, the Zodiac Killer sent a card to the San Francisco Chronicle containing a 340-character secret message that for more than 50 years went unsolved by detectives, cryptography experts, amateur sleuths and curious others.

Wonder no more, true-crime aficionados. 

After months of crunching code during the pandemic, three researchers on three different continents announced that they’d finally decoded the message. Further bolstering the claim, experts at the FBI verified the solution (and even tweeted about it). The encrypted message didn’t reveal the identity of the Zodiac, but it did bring decades of speculation, conspiracy theories and guesswork to a dramatic close.

Cracking the Code

“It took a lot of computational effort, and it’s been a real source of frustration for a lot of people,” says computer programmer David Oranchak in Roanoke, Virginia, who has a background in cryptography and coordinated the effort. He’s spent years fielding theories from misguided, would-be sleuths about the meaning of the 340-character code and the identity of its author. “So many people conjure coincidences out of thin air, and the more coincidences they generate, the stronger their evidence.” 

“This cipher has always had such a target on its back,” says Sam Blake, an applied mathematician at the University of Melbourne who worked with Oranchak. 

Although the codebreakers involved had each been working on the cipher for years, the successful joint effort began in 2018 when Oranchak delivered a talk about the cipher at the annual meeting of the American Cryptogram Association in Asheville, North Carolina. He posted the talk on YouTube where, predictably, it elicited hundreds of comments, many of which came from people who (erroneously) claimed they’d already solved it.

Read more in the January/February 2022 issue of Discover magazine.