The Zodiac Killer Ciphers

The Zodiac Killer sent at least four cryptographic ciphers to San Francisco Bay Area newspapers between 1969 and 1970, claiming that the ciphers contained his identity and promising to kill more victims if they were not published. The ciphers — known as the 408 cipher, the 340 cipher, the 13-character cipher, and a shorter fragment — became as famous as the murders themselves, attracting decades of cryptanalytic attention from professional codebreakers, amateur enthusiasts, and academic researchers.

The 408-character cipher, split across three pieces and sent to three newspapers simultaneously in July 1969, was solved within a week by a high school teacher named Donald Harden and his wife Bettye. The message was a rambling statement about killing giving the Zodiac thrills and claiming his victims would be his slaves in the afterlife — chilling but containing no identifying information. The other ciphers proved far more resistant.

The 340-character cipher — named for its length and long considered the most likely to yield meaningful content — was solved in December 2020 by David Oranchak, a software developer, working with Australian mathematician Sam Blake and Belgian computer scientist Jarl Van Eycke. The solution required recognizing that the cipher had been deliberately scrambled by reading it in an unusual pattern. The decoded message again provided no name, only more taunting: "I hope you are having lots of fun in trying to catch me." The 13-character cipher, which the Zodiac claimed spelled his name, has never been solved despite enormous effort.

The Zodiac ciphers occupy a unique intersection of cryptography, true crime, and popular culture. They have inspired academic papers, software tools, international competitions, and the dramatic centerpiece of David Fincher's "Zodiac." The persistent failure to solve the 13-character cipher — which may or may not actually contain a name — means the killer's identity remains locked in code, his final taunt to investigators still unbroken more than fifty years later.