Beginning in 1969, a series of taunting letters from a killer calling himself the Zodiac began arriving at San Francisco Bay Area newspapers. The correspondence contained chilling details of his crimes, threats of future violence against targets like schoolchildren, and a distinctive cross-circle symbol he used as a signature. Interspersed within the missives were four complex cryptograms, which he claimed would reveal his identity; two of these ciphers remain unsolved to this day. Despite providing specific information only the perpetrator could know and directly engaging with law enforcement and the public, the author of these letters was never identified, and the communications ceased as abruptly as they had begun, leaving his true name and motive unknown.