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How Mathematicians Cracked the Zodiac Killer’s Cipher

After half a century of relentless pursuit, a trio of codebreakers finally cracks the Zodiac Killer code, earning the coveted nod of approval from the FBI.

By Stephen Ornes
Oct 31, 2023 4:15 PMMar 25, 2024 5:54 PM
Coded letter sent by the Zodiac killer to the San Francisco Chronicle in 1969.
Coded letter sent by the Zodiac killer to the San Francisco Chronicle in 1969 (Credit: Bettmann Archive/Getty Images)

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Few cases have captured the public's imagination and baffled investigators quite like the Zodiac Killer. For decades, this unidentified serial murderer taunted law enforcement and the public alike with cryptic messages and ciphers, leaving a trail of terror in his wake.

One of the most infamous aspects of the Zodiac's sinister saga was the series of letters he sent to local newspapers, in which he claimed responsibility for his gruesome crimes and taunted authorities with cryptograms. Among these letters, one stood out as a tantalizing puzzle that would endure for years – the Zodiac Killer letter that finally got decoded.

 Wonder no more, true-crime aficionados. 

 Who Is the Zodiac Killer?

In the late 1960s, a serial killer self-identifying as “the Zodiac” killed at least five people in Northern California and claimed to have murdered more. In November 1969, the Zodiac Killer sent a card to the San Francisco Chronicle containing a 340-character secret message that for more than 50 years went unsolved by detectives, cryptography experts, amateur sleuths, and curious others.

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