In 1969 an uncaught serial killer mailed newspapers a 340-character cipher and dared the world to read it. For half a century the best minds at the NSA and FBI failed. Then in December 2020 three hobbyists — a web developer, a mathematician, and a warehouse coder — quietly solved it from their spare rooms. Here's how.
Start with the killer himself: the confirmed Bay Area murders of 1968–69, the taunting letters signed with a crosshair, and the four ciphers he mailed to the press. Two are still unsolved.
The moment it broke. David Oranchak, one of the three solvers, narrates exactly how the Z340 finally gave way — and reads the chilling message that had been hiding in plain sight for 51 years.
The contemporary announcement from the cryptography community, laying out the trick: a 'knight's move' transposition scrambling the reading order, stacked on top of a homophonic substitution — two puzzles in one.
The tooling behind the win: AZDecrypt, software that can attempt up to 200 homophonic ciphers per second, and how a decades-long crowd of amateurs set the stage for the final three to finish it.
Reverse-engineering the killer's own process. Oranchak reconstructs how the Zodiac physically built the cipher — the mistakes, the deliberate misdirection, and why it was so brutally hard to unscramble.
The retrospective. Half a decade on, what the solution did and didn't reveal — and the two remaining Zodiac ciphers, Z13 and Z32, that supposedly hide the killer's name and are still completely unbroken.