The Zodiac Killer's Cipher Took 51 Years to Crack

The Letters Begin

On July 31, 1969, three Bay Area newspapers each received a letter in the morning mail. The San Francisco Chronicle, the San Francisco Examiner, and the Vallejo Times-Herald. Each letter contained a cover note demanding the newspaper print the enclosed material on its front page, threatening further killings if it refused. Each letter also contained one third of a 408-character cipher -- a grid of strange symbols, homophones, and inverted letters that no recipient could immediately read.

The cipher was a substitution cipher: each symbol represented a letter, but the same letter could be encoded by multiple different symbols, making standard frequency analysis harder. Whoever built it had studied the field. The 408 characters were split three ways so that no single newspaper, acting alone, could decode the whole message. To read it, all three had to print their segment. They did.

But the letters had started earlier. On the night of December 20, 1968, two teenagers were shot and killed at a rural turnout on Lake Herman Road near Vallejo, California. Betty Lou Jensen, sixteen, and David Faraday, seventeen, were on a first date. Neither had been robbed. No witness came forward. Six months later, on July 4, 1969, a man approached a car parked near Blue Rock Springs Park, also in Vallejo, and opened fire. Darlene Ferrin, twenty-two, died. Her companion, Michael Mageau, survived with severe wounds and later described the shooter: stocky, with light-colored hair, wearing glasses. He estimated the man was between twenty-five and thirty years old.

Two weeks after the Blue Rock Springs shooting, the same man -- or someone claiming to be him -- called the Vallejo Police Department from a pay phone. He reported both shootings in a flat, unemotional tone, said he was responsible, and provided details that were not public knowledge. The call was traced to a booth near the sheriff's office. Nobody was waiting there when police arrived.

The July 31 letters were the killer's first contact with the press. He signed each one with the same symbol: a circle bisected by a crosshair. He called himself the Zodiac.

The First Cipher: One Week, a Kitchen Table

The challenge of a three-part 408-character cipher sent to three separate newspapers might have stumped a police cryptography unit for months. It took Donald and Bettye Harden approximately one week. Donald was a high school history and civics teacher from Salinas, California. Bettye was a homemaker. Neither had formal cryptanalysis training. They read about the cipher in the newspaper and decided to try it at home.

Bettye's approach was psychological as much as mathematical. She assumed the killer was egotistical -- that he would begin with the word "I" and would use the word "kill." She searched for repeating patterns in the cipher that matched those letter sequences and worked outward. Within days, the substitution key was reconstructed almost entirely. The message it revealed was unambiguous:

"I like killing people because it is so much fun. It is more fun than killing wild game in the forrest because man is the most dangertue anamal of all. To kill something gives me the most thrilling experence it is even better than getting your rocks off with a girl. The best part of it is thae when I die I will be reborn in paradice and all the I have killed will become my slaves. I will not give you my name because you will try to sloi down or stop my collecting of slaves for my afterlife."

-- Zodiac Killer, Z408 cipher, solved July 1969

The misspellings were intentional. The killer was educated enough to construct a workable cipher; the errors in the plaintext were almost certainly deliberate misdirection, meant to complicate any linguistic analysis of his writing style. The final eighteen characters of the Z408 were never decoded -- they appear to have been a second layer of encryption, possibly encoding a name, and the Hardens' key did not reach them. Neither has anyone else's, in the fifty-seven years since.

The newspapers published the cipher and its solution. The Zodiac wrote again on August 7, 1969, this time in plain English, to confirm the solution was correct and to introduce himself by name for the first time. "I am the Zodiac," the letter began.

The Murders Continue

On September 27, 1969, a man approached two college students picnicking at Lake Berryessa in Napa County. He was wearing a black hood with a bib-like panel on the chest bearing the Zodiac's crosshair symbol, stitched in white. He tied Bryan Hartnell and Cecelia Shepard with pre-cut lengths of rope he had brought with him, then stabbed both of them repeatedly. Hartnell survived. Shepard died two days later. Before leaving, the attacker picked up a felt-tip marker and wrote on the door of Hartnell's white Volkswagen: the dates of the previous Vallejo attacks, the Lake Berryessa date, and the words "by knife."

Hartnell survived and gave the clearest physical description yet: the hood, the bib, the Zodiac symbol. He described the man's voice as even and without particular accent. He estimated the man was between twenty-five and thirty years old and weighed around two hundred pounds.

Two weeks later, on October 11, 1969, a cab driver named Paul Stine was shot once in the head at the corner of Washington and Cherry Streets in the Presidio Heights neighborhood of San Francisco. The Zodiac had taken a portion of Stine's shirt. He later mailed a piece of it to the Chronicle as proof. Witnesses in an upstairs window of a nearby house saw a heavyset white man with glasses wiping down the interior of the cab. They called police. The dispatcher relayed the description incorrectly, reporting the suspect as a Black male. Officers who encountered a man matching the actual description on the street minutes later waved him through.

The Zodiac claimed in his letters to have killed as many as thirty-seven people. Investigators have confirmed five deaths attributable to the known attacks. Other cold cases from the period have been proposed as possible Zodiac crimes -- investigators have never formally linked them.

The 340 Cipher: 51 Years of Failure

On November 8, 1969, the Zodiac sent a new letter to the San Francisco Chronicle. It included a card with a hand-drawn figure of a man and a dripping pen -- a theatrical flourish -- and a second cipher. This one was 340 characters. It became known as Z340.

The FBI's Cryptanalysis and Racketeering Records Unit attempted to decode Z340 immediately. Professional cryptanalysts worked it. Hobbyists worked it. Amateur enthusiasts built software tools specifically for it. The cipher appeared to use a substitution system similar to Z408, but nothing that worked on Z408 worked on Z340. Standard frequency analysis produced noise. The most plausible partial solutions never yielded coherent English. For half a century, Z340 was treated as either a more sophisticated cipher or possibly a deliberate hoax -- symbols arranged to look like a solvable cipher while containing no actual message.

The critical insight came in 2020. David Oranchak, a software developer in Virginia who had been studying the Zodiac ciphers for years, identified something earlier analysts had largely dismissed: the cipher incorporated transposition. The Zodiac had not only substituted symbols for letters. He had also rearranged the order of the symbols before writing them down -- reading the cipher diagonally, or in some other non-standard sequence -- which meant any substitution key applied in the standard left-to-right, top-to-bottom order would produce garbage.

Oranchak partnered with Sam Blake, an applied mathematician in Melbourne, Australia, and Jarl Van Eycke, a programmer in Belgium, whom he had connected with through online cipher-research communities. Blake generated 650,000 variations of the Z340 ciphertext, each reflecting a different possible reading order or transposition pattern. Oranchak fed every variation through AZdecrypt, Van Eycke's purpose-built code-breaking software. On December 3, 2020, one of Blake's 650,000 arrangements, combined with the right substitution key, produced readable English.

The team submitted the solution to the FBI on December 5, 2020. The FBI confirmed it publicly on December 11. The decoded message read:

"I hope you are having lots of fun in trying to catch me that wasnt me on the tv show because I am too clever for that. I am not afraid of the gas chamber because it will send me to paradice all the sooner because I now have enough slaves to work for me where everyone else has there hands tied behind their backs and is waiting for me i am not worried at all about my name because no one will find me i am to clevar for them."

-- Zodiac Killer, Z340 cipher, decoded December 2020

The misspellings -- "paradice," "clevar," "wasnt" -- mirror the errors in Z408. The message confirmed the killer was still alive and confident in late 1969. It referenced a television appearance, widely understood to refer to an October 1969 episode of The Jim Dunbar Show in which a man claiming to be the Zodiac called in during a live broadcast. The decoded message denied it was him. It contained nothing that advanced the investigation: no name, no location, no identifying detail.

Oranchak's comment after the solution went public was direct: "The message doesn't really say a whole lot."

The Cipher That May Never Open

Among the Zodiac's letters was a short cipher that began, in plain English: "My name is --" followed by thirteen encrypted characters. It became known as Z13.

Z13 has been subjected to the same computational and analytical methods that eventually cracked Z340. Nothing has worked. The leading interpretation among cryptanalysts is that the thirteen characters do not encode a real name at all -- that they are a red herring, a deliberate construction designed to look solvable while containing no valid plaintext. The Zodiac was methodical enough to split his first cipher into three parts and mail them simultaneously. A cipher that appeared to contain his name but decoded to nothing would be consistent with that level of premeditation.

A fourth cipher, Z32, was sent in April 1970. It purportedly described the location of a bomb. It has not been solved and no bomb was found.

The Dripping Pen Card

The November 8 letter that contained Z340 also included what investigators called the "Dripping Pen Card." It was a greeting card, modified by hand, with a figure holding a pen that dripped what appeared to be blood. The card included references to collecting slaves and a score-keeping list: "Slaves I will collect for my afterlife." The theatricality was consistent across all his correspondence -- the Zodiac understood that the letters themselves, not just their content, were part of a public performance.

The Zodiac continued writing through at least 1974. He claimed responsibility for additional killings that were never confirmed. His letter count reached approximately twenty-one verified communications. The content grew more erratic, the claims less specific, the tone more performative. Whether the later letters represented the same person is a question investigators have debated without resolution.

The Suspects

The investigation produced hundreds of suspects over the decades. One dominated law enforcement attention for years: Arthur Leigh Allen, a former schoolteacher and convicted sex offender from Vallejo. Allen was investigated repeatedly beginning in 1971. Associates reported that he had expressed disturbing fantasies consistent with the killer's letters. He wore a Zodiac-brand watch with a crosshair symbol on the face. He had been near Lake Berryessa around the time of the Shepard attack. He matched the physical description given by Hartnell and Mageau.

Allen was interviewed multiple times, his homes searched, his typewriter and handwriting analyzed. The handwriting did not match. The typewriter was not the source of the letters. Then, in 2002, investigators extracted DNA from saliva on stamps and envelope flaps from several Zodiac letters. The partial male profile recovered did not match Arthur Leigh Allen. Allen had died in 1992, before the DNA extraction, and was never charged. He remains the most frequently named primary suspect, with the caveat that the DNA evidence points elsewhere -- unless the Zodiac had someone else lick the envelopes.

Other suspects have been proposed by independent researchers: Richard Gaikowski, a San Francisco journalist; Lawrence Kane, a Nevada man with connections to the Bay Area. None have produced the kind of corroborating evidence that could close the case. The partial DNA profile obtained in 2002 is insufficient for a conviction on its own and has not matched any profile in available databases.

Why the Case Remains Open

The Zodiac investigation has never formally closed because no identifying evidence has crossed the threshold required to name a perpetrator. There are no fingerprints from the crime scenes that match any known individual. The DNA profile from the letters is partial -- it establishes that the person who licked the envelopes was male, but it cannot be used to confirm identity without a complete profile to compare it to. The composite sketches produced from witness accounts show a heavyset white man with glasses and short hair, a description that applied to a substantial fraction of the adult male population of the Bay Area in 1969.

The survivors -- Michael Mageau and Bryan Hartnell -- both described their attacker. Mageau, in a 2009 interview, identified Arthur Leigh Allen from a photo lineup. But Mageau's identification came four decades after the attack, and Allen's DNA did not match the letters. Courts have treated the case as effectively unresolvable absent new physical evidence.

The San Francisco Police Department and the Napa County Sheriff's Office have both maintained open case files. As of 2026, no arrest has been made. The Zodiac's identity is officially unknown.

What is known: the ciphers. The Z408, cracked in a week by a teacher and his wife at a kitchen table in 1969. The Z340, defeated for fifty-one years, finally yielding in December 2020 to three hobbyists on three different continents who had never met in person. The Z13, thirteen characters that begin with "My name is" and have told no one anything in more than fifty years. The crosshair symbol on every letter. The careful splitting of that first cipher so that no single newspaper could read it alone.

Whoever he was, he thought carefully about how to be remembered.