Zodiac Killer Ciphers
A serial killer taunted police with coded letters. One cipher wasn't solved for 51 years. Another remains unsolved. 'I like killing people because it is so much fun,' he wrote. His identity is still unknown.
The Zodiac Killer terrorized the San Francisco Bay Area in the late 1960s and early 1970s, taunting police and newspapers with cryptic ciphers. His identity remains unknown.
The Killer
According to documented records:
The Zodiac Killer:
- Murdered at least five people (possibly more)
- Active 1968-1969 (possibly later)
- Sent encrypted letters to newspapers
- Used a crosshair symbol as his signature
- Claimed 37 victims (unconfirmed)
- Was never caught
The Ciphers
The Zodiac sent four main ciphers:
408 Cipher (1969): Solved within a week by a school teacher and his wife. It read: “I like killing people because it is so much fun.”
340 Cipher (1969): Not solved until 2020—51 years later—by amateur codebreakers.
13 Character Cipher: May contain his name. Unsolved.
32 Character Cipher: Possibly his name. Unsolved.
The 340 Solution
In 2020, a team cracked the 340 cipher:
- It took 51 years
- Used sophisticated computer methods
- The message was rambling but coherent
- It didn’t reveal his identity
- The FBI confirmed the solution
The Letters
The Zodiac’s communications:
- Included threats to bomb school buses
- Referenced killing for “thrills”
- Contained his crosshair symbol
- Mocked police efforts
- Created public terror
Suspects
Many have been suspected:
- Arthur Leigh Allen (most prominent)
- Various others proposed over decades
- DNA and fingerprints haven’t matched conclusively
- The case remains officially unsolved
The Cipher Methods
The codes used:
- Homophonic substitution (multiple symbols per letter)
- Deliberate misspellings
- Symbol-based encryption
- Designed to frustrate decryption
Why It Matters
The Zodiac case:
- Inspired films (“Dirty Harry,” “Zodiac”)
- Pioneered criminal cryptography
- Demonstrates the difficulty of codebreaking
- Remains one of America’s most famous unsolved cases
Modern Technology
Despite advances:
- DNA has been tested
- Genealogy databases have been searched
- Computer analysis has been applied
- The killer’s identity remains unknown
The Unsolved Ciphers
The remaining codes:
- May contain his name
- Are too short for reliable analysis
- Could be unsolvable without the key
- Continue to attract amateur cryptographers
Legacy
The Zodiac Killer:
- Became a cultural touchstone
- Inspired countless theories
- Demonstrates limits of investigation
- May never be identified