The Zodiac Killer is a serial killer responsible for at least five murders in Northern California from 1968 to 1969, according to Britannica. He would often tease authorities and the media by penning cryptic letters. In an early letter to the press in 1969, he concealed his real identity by giving himself the name Zodiac. He would continue to send letters up until 1974 that included ciphers or cryptograms. He typically began each letter with the phrase: “This is the Zodiac speaking.”

Shortly after his murdering stint, a pair of private citizens were able to decode one of his ciphers to read: “I like killing people because it is so much fun.” However, other ciphers sent by the Zodiac Killer took decades to decode.

One cipher that was mailed to the San Francisco Chronicle in November 1969 was finally decoded in December 2020 by a small team that consisted of a software developer, an applied mathematician, and a computer programmer, according to the New York Times. Its message reads: “I hope you are having lots of fun in trying to catch me" and “I am not afraid of the gas chamber."