READING · 5 MIN
TWO CODES FELL.
ONE STILL WON'T.
An unidentified killer active in Northern California in the late 1960s mailed newspapers four separate ciphers. Two have been broken - one in a week, one after 51 years. The case itself remains unsolved. This is presented as real, historical true-crime.
Four ciphers, mailed to newspapers â—˘
Beginning in 1969, a killer who signed his letters “Zodiac” sent taunting messages to Bay Area newspapers, several containing enciphered text built from invented symbols rather than plain letters. Four separate ciphers are attributed to him, now generally referred to by their length: Z408, Z340, Z13, and a shorter, disputed fragment. The killer was never identified and no one has ever been charged.
Z408: broken in a week, by a schoolteacher couple â—˘
The first cipher, 408 characters long, was split across three letters mailed to three different Bay Area papers in July 1969. It was solved within about a week by Donald and Bettye Harden, a schoolteacher couple in Salinas, California, working the puzzle by hand at their kitchen table. It turned out to be a homophonic substitution - several different symbols could stand in for the same letter, a step up in complexity from a straightforward one-to-one mirror like Atbash- and decoded into a rambling message about the killer's stated motive, riddled with his own misspellings.
Z340: unsolved for 51 years â—˘
A second, 340-character cipher was mailed in November 1969 and resisted every attempt at decryption for over five decades. In December 2020, an international team of private citizens - Belgian programmer David Oranchak, Australian mathematician Sam Blake, and Belgian programmer Jarl Van Eycke - broke it using custom-built software combined with manual cryptanalysis, working independently of any law enforcement agency. The FBI confirmed the solution. Like Z408, the decoded text was another taunting message, with no new information about the killer's identity.
Z13: still unread â—˘
A much shorter cipher - just 13 characters, sent in a 1970 letter that opened with the words “My name is” - has never been broken. It's the shortest of the four, which makes it mathematically the hardest: too little ciphertext for the frequency patterns that cracked the longer two to show up reliably. Whatever name, if any, sits behind those 13 symbols remains exactly as unread today as it was when it arrived.
Play the ciphers in this story