How the Zodiac Killer’s Infamous 340 Cipher Was Decoded by Private Citizens After 51 Years
For decades, the Zodiac Killer’s 340-character cipher, mailed to the San Francisco Chronicle in 1969, remained unsolved. By that time, the killer had terrorized Northern California and was responsible for at least 5 confirmed murders, while claiming more in letters to police and newspapers. The cipher mixed symbols, circles, and crosshairs, and some letters were left unencrypted while others were substituted with symbols. This uneven structure confused investigators and stalled efforts. The Zodiac also contacted police after attacks, using the cipher to taunt authorities and the public.
In December 2020, after about 4 months of focused work, an international team of amateur codebreakers solved the cipher. The team included David Oranchak, a software engineer from the United States; Sam Blake, a mathematician from Australia; and Jarl Van Eycke, a data analyst from Belgium. Using computer programs and pattern analysis, they tested how symbols aligned with letters, spacing, and line breaks. They broke the cipher into sections, tracked repeated symbols, and compared them to the Zodiac’s earlier 408-character cipher and his previous letters sent to the San Francisco Chronicle and San Francisco Examiner. By studying how words, spelling errors, and phrasing appeared in those earlier messages, they identified familiar patterns. The team examined symbol frequency, diagonal and vertical reading paths, ruled out incorrect solutions, and confirmed the final decoding produced consistent, readable sentences.
Lines included: “I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME” and “I AM NOT AFRAID OF THE GAS CHAMBER.” The solution revealed no new suspects or victim details.
The FBI confirmed the cipher was solved by private citizens. The Zodiac Killer case remains officially open. See comments for the full 340 cipher solution.
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