The Zodiac Killer’s 340 Cipher: Finally Cracked After 51 Years

What if I told you that everything you learned in school about this topic is incomplete? The Zodiac Killer’s 340 Cipher—but the deeper I dug, the more convinced I became that this is one of the most fascinating stories in recent memory.

51 Years of Failure

The 340-character cipher, mailed to San Francisco newspapers in 1969, replaced the earlier 408-character cipher that had been solved within days. But this second cipher remained unsolved for over five decades despite efforts by the FBI, CIA, NSA, and thousands of amateur sleuths. Some even wondered if it was a hoax.

The Breakthrough

In December 2020, Australian software engineer Sam Blake, American mathematician Jarl Van Eycke, and Belgian programmer David Oranchak finally cracked it. The key insight was that the cipher combined TWO techniques: homophonic substitution (multiple symbols for the same letter) AND transposition (rearranging columns before reading). Previous solvers had tried one or the other.

But here’s where it gets really interesting.

What It Said

The decoded message read: ‘I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME… I AM NOT AFRAID OF THE GAS CHAMBER BECAUSE IT WILL SEND ME TO PARADISE ALL THE SOONER.’ The tone was consistent with the Zodiac’s earlier communications.

Validation

The FBI officially confirmed the solution’s validity in 2020. While the cipher didn’t reveal the killer’s identity, it proved that modern computational methods combined with historical cipher analysis can solve problems that elite government agencies could not.

Key Takeaways

• The Zodiac Killer’s 340-character cipher was cracked in December 2020 after 51 years.
• The solution was found by a team of amateur codebreakers, not government agencies.
• The decoded message referenced the ‘gas chamber’ and taunted authorities.
• The FBI officially confirmed the solution’s validity in 2020.

Perhaps the real question isn’t what happened, but what it means for us today.