Zodiac Killer letters sent to the San Francisco Chronicle (Z340 cipher)

Beginning in 1969 the Zodiac Killer sent multiple letters to Bay Area newspapers, including the San Francisco Chronicle. One of those letters, called the Z340 cipher, was mailed to the Chronicle on November 8, 1969 and remained unsolved until a team of codebreakers announced a solution in December 2020. The Zodiac case remains officially unsolved and the killer's identity has not been conclusively established.