What Are the Zodiac Killer Letters
The Zodiac Killer sent multiple coded letters to San Francisco Bay Area newspapers and police departments between 1968 and 1974. These letters contained taunting messages, cryptograms, and claims of responsibility for murders. The case remains open in several jurisdictions, and the FBI maintains a public file with many of these documents.
The letters became a central part of the investigation because they included specific details only the perpetrator could know. Investigators used forensic linguistics, handwriting analysis, and cipher decryption to try to identify the author. The FBI page on the Zodiac case provides an overview of the letters and related evidence.
Key Letters and Ciphers in the Zodiac Killer Case
The most famous document is the Z408 cipher, a 408-character substitution code sent to the San Francisco Chronicle in 1969. The killer also mailed a 340-character cipher, known as Z340, which remained unsolved for over 50 years before amateur codebreakers cracked it in 2020.
Unsolved Ciphers and Decoding Efforts
Z13 and Z32 are two shorter ciphers that have not been fully decoded. The FBI's Cryptanalysis and Racketeering Records Section has worked on these codes, and the San Francisco Police Department still lists the Zodiac letters as active evidence.
Current Status of the Zodiac Killer Letters
Many original letters are held by the San Francisco Police Department, the FBI, and the Vallejo Police Department. In 2024, investigators continued to receive tips and conduct DNA analysis on envelope seals and stamps from mailed letters.
The case is also the subject of ongoing research by independent cryptographers and true crime analysts. Some documents have been released through public records requests, while others remain restricted. The FBI's main page on the Zodiac case outlines which materials are available to the public.