In the summer of 1969, a killer terrorizing Northern California made an unusual demand: publish my coded message on your front page, or I will keep killing. Newspapers complied, and one of the most enduring puzzles in American crime was born. More than half a century later, people still ask which Zodiac Killer ciphers are still unsolved — and why some of the sharpest cryptographers on Earth have failed where a teacher and his wife once succeeded. The answer sits somewhere between clever encryption, taunting misdirection, and pure human ego.
The Four Ciphers the Zodiac Sent
The Zodiac Killer produced four distinct coded messages, each referred to by its character count. The first, the 408 cipher, arrived in three parts mailed to the San Francisco Chronicle, the Vallejo Times-Herald, and the San Francisco Examiner in July 1969. The second, the 340 cipher, followed in November 1969 and became the most notorious of all. Two shorter messages — the 13-character cipher (also called the “My name is” cipher) and the 32-character cipher — appeared in 1970.
Each used a homophonic substitution system, meaning a single letter of plaintext could be represented by several different symbols. This design deliberately flattens the natural frequency of common letters like E and T, making the codes far harder to break than a simple one-to-one substitution. The Zodiac clearly understood at least the basics of amateur cryptography — a detail investigators have chewed on for decades.
The Codes That Were Actually Cracked
Not every message resisted. The 408 cipher was solved within days — not by the FBI or the CIA, but by Donald Harden, a high school teacher in Salinas, and his wife Bettye. Bettye guessed that an egotistical killer would likely begin with the word “I” and use “KILL” or “KILLING.” That hunch cracked it open. The decoded message began, chillingly, “I LIKE KILLING PEOPLE BECAUSE IT IS SO MUCH FUN.” Yet it contained no name and no verifiable clue to identity — just boasting and a garbled reference to collecting “slaves” for an afterlife.
The far more resistant 340 cipher held out for 51 years. In December 2020, an international team — American software developer David Oranchak, Australian mathematician Sam Blake, and Belgian programmer Jarl Van Eycke — announced they had solved it, and the FBI confirmed the result. The message was another rant, mocking the police and again offering nothing that pointed to a suspect. The breakthrough required understanding that the killer had read the code in an unusual diagonal pattern, layered with encoding quirks that defeated straightforward computer attacks for years.
Why the Remaining Ciphers Resist Solutions
So which Zodiac Killer ciphers are still unsolved? The short 13-character and 32-character messages remain officially uncracked, and there are practical reasons why. The biggest is length. Codebreaking, whether by hand or by machine, relies on statistical patterns — repeated symbols, common letter pairings, structural clues. A 13-symbol string is simply too short to generate reliable statistics. There are millions of plausible plaintext solutions, and no way to prove which, if any, is correct.
The 13-cipher allegedly answers the question of the killer’s name, since it followed the taunt “MY NAME IS.” Amateur sleuths have forced it to spell out dozens of candidate names over the years, but every “solution” requires assuming the answer first and reverse-engineering the symbols to fit — the opposite of legitimate decryption. It is also entirely possible the Zodiac never encoded a real name at all, and the message is deliberate nonsense designed to keep investigators chasing shadows.
The Ego Behind the Encryption
What makes the Zodiac case so magnetic is the psychology stitched into the ciphers. Here was someone who craved attention so badly that he threatened murder to see his codes printed, yet who repeatedly declined to identify himself when he seemingly promised to. That contradiction fuels a key theory: the ciphers may have been performance as much as communication. The killer wanted the world puzzling over him, and an unsolved code guarantees permanent relevance in a way a solved one never could.
This pattern of manipulation echoes across many of the most disturbing cold cases, where the offender treats the investigation itself as a game. If you’re drawn to how criminals weaponize publicity, our breakdown of famous unsolved cold cases and their missing clues explores similar mind games in other investigations.
What Modern Technology Can and Cannot Do
After the 340 solution, hope surged that artificial intelligence and modern computing might finally finish the job. The reality is more sober. Software like Van Eycke’s AZdecrypt can test billions of possibilities, but it needs enough ciphertext to distinguish a genuine solution from a statistical fluke. The short ciphers don’t provide that. Even a perfect algorithm cannot manufacture information that was never there.
There’s also the unresolved question of whether the remaining messages are even valid ciphers. Some experts suspect the 13- and 32-character notes could be hoaxes within a hoax — decoy symbols with no consistent underlying key. And with the Zodiac’s identity never confirmed and the trail cold since the 1970s, there may be no external evidence left to check a proposed answer against. Technology has narrowed the mystery, but it cannot force a locked box to open when we can’t be sure there’s anything inside.
Watch the Full Investigation on Dark CasesTV
The Zodiac’s ciphers are only one thread in a case tangled with letters, taunts, and suspects who were investigated and cleared. The full story — the victims, the manhunt, the near-misses, and the codes that still tease researchers today — deserves to be told in depth. Head over to the Dark CasesTV YouTube channel, where we walk through the timeline, the evidence, and the theories with the care a case this complex demands. Subscribe and dive into our deep-dive true-crime investigations, and decide for yourself whether the Zodiac’s remaining ciphers hide a name — or nothing at all.
Enjoyed this? More videos on the Dark CasesTV YouTube channel.