Zodiac Killer letters sent to the San Francisco Chronicle

Between 1969 and 1970 an unknown assailant who identified himself as the "Zodiac" sent multiple taunting letters and encrypted ciphers to the San Francisco Chronicle and other Bay Area newspapers. One famous submission, the 340-character cipher, was mailed to the Chronicle and remained unsolved until December 2020 when amateur codebreakers announced a solution. The letters and ciphers were physically received and handled by the newspaper's offices during the original investigation. The events are part of an unsolved serial-killer case that occurred across multiple Bay Area locations.