51 years. 340 symbols.

In 1969, a 340-character cipher attributed to the Zodiac Killer was mailed to the San Francisco Chronicle. Its symbols resisted a confirmed solution for 51 years.

In 2020, David Oranchak, Sam Blake and Jarl van Eycke solved it. They combined software with a search for the order in which the symbols should be read: changing letters alone was not enough.

Their solution was submitted to the FBI on 5 December 2020 and subsequently confirmed. Decoding a message and identifying its author are separate investigative questions.