The case of the Zodiac Killer is one of the most widely known unsolved serial killer cases in history. The Zodiac is the pseudonym of an unidentified serial killer who murdered at least five people in the San Francisco Bay Area between December 1968 and October 1969. The Zodiac attacked three couples and a cab driver in Benicia, Vallejo, unincorporated Napa County, and the city of San Francisco. Despite several theories about the Zodiac's true identity, the only suspect police named was Arthur Leigh Allen, a former elementary school teacher and convicted sex offender who died in 1992.
The Zodiac's murders, cryptograms, and letters to newspapers have made the case one of the most famous unsolved cases in American history. In 2004, the San Francisco Police Department marked the case "inactive," but subsequently re-opened the case in 2006. Police and investigators concur The Zodiac attacked seven people on four occasions in California.
Besides his murders, Zodiac was known for his use of ciphers. The first Zodiac cipher was solved within a week of its publication, while the second cipher was solved by the authors after 51 years, when it was discovered to be a transposition and homophonic substitution cipher with unusual qualities.
The Zodiac Killer: Fact vs Myth
The Victims
- The first murders retroactively attributed to the Zodiac were the shootings of high school students Betty Lou Jensen (16) and David Arthur Faraday (17) on December 20, 1968.
- Darlene Ferrin (22) and Michael Mageau (19) were shot shortly after midnight on July 4, 1969.
- On September 27, 1969, Pacific Union College students Bryan Hartnell (20) and Cecelia Shepard (22) were picnicking at Lake Berryessa on a small island connected by a sand spit to Twin Oak Ridge.
- The last confirmed Zodiac murder took place two weeks after the Lake Berryessa attacks. on October 11 in downtown San Francisco, the Zodiac hailed a cab which was driven by a doctoral student named Paul Stine.
The first letters were sent to three papers in the Bay Area, each containing a different part of the cipher. After the first message, the killer’s ciphers became more complicated. Two of the Zodiac's four cryptograms were decrypted in 1969 and 2020, and the other two remain unsolved. The Zodiac's last letter was received by the San Francisco Chronicle in 1974.
From 1969 to 1974, the Zodiac sent over twenty letters to newspapers, police, Chronicle writer Paul Avery, and attorney Melvin Belli. Here are some of the dates when the Zodiac sent letters:
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- July 31st 1969: San Francisco Chronicle, San Francisco Examiner, and Vallejo Times. One-third of "Z408 cryptogram" enclosed with each letter.
- August 4th 1969: Examiner.
- October 13th 1969: Chronicle. Swatch of Paul Stine's shirt.
- November 8th 1969: Chronicle. "Z340 cryptogram." The "Dripping Pen" card.
- November 9th 1969: Chronicle. Bomb diagram.
- December 20th 1969: Melvin Belli. Swatch of Stine's shirt.
- April 20th 1970: Chronicle.
- April 28th 1970: Chronicle. Greeting card.
- June 26th 1970: Chronicle.
- July 24th 1970: Chronicle.
- July 26th 1970: Chronicle.
- October 5th 1970: Chronicle. Thirteen-hole punch card.
- October 27th 1970: Paul Avery at Chronicle. Halloween card.
- March 13th 1971: Los Angeles Times.
- January 29th 1974: Chronicle.
The Ciphers
Cryptographic researchers have finally cracked a 51-year-old code left by the Zodiac, a serial killer who terrorized Northern California in the late 1960s and early 1970s. Over the years, many have tried to solve the 340-character message received by the San Francisco Chronicle on October 14, 1969. David Oranchak, Sam Blake, and Jarl Van Eycke used software to help them break the cipher, first by finding the many possible reading directions that could be used if the cipher was transpositional. By starting in the top left hand corner, then moving down one line and across two spaces to get the next letter, a key which could be translated into letters and then words emerged. The letter “B” for instance, was represented by “?7”, “c” by a simple “9” and “A” by a whole load of symbols unavailable on a keyboard.
The first cipher, Z408, was cracked by Donald and Bettye Harden. The decoded message did not reveal the Zodiac's identity. On August 5, it was cracked by Donald and Bettye Harden, a couple in Salinas. Neither was a cryptologist. The message was rife with misspellings and referred to Richard Connell's 1924 short story "The Most Dangerous Game". The Zodiac explained killing was a way of collecting slaves for his afterlife.
The second cipher, Z340, remained unsolved for 51 years. Z340 was deciphered by an international team of private citizens on December 5, 2020.
The Decryption Process
They tried various direct transposition methods involving a direct offset of 18 or 19 characters. They looked for interesting patterns by transposing characters from the top-right corner, from the top-left corner, outside in, and inside out. Nothing. They tried one-step transpositions (moving down one row) two-step transpositions (down one row, then over two columns, etc.). Still nothing. They tried counting repeating bigrams, or pairs of symbols. Nothing.
Finally, they tried combining all one- and two-step transpositions and repeating bigrams at the same time. “Then we considered testing all 3-tuples of transpositions,” Blake wrote in a March 2021 blog entry on the Wolfram site. “However, this would require testing 155,929,364,660,224 candidate ciphers. Naively checking one a second would take over five million years. So we limited our experiments to decimations which would be reasonable to write out by hand and then only tested candidates with a high bigram count.
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The researchers then decided that perhaps the key was breaking up the 340-character cipher. They split the cipher horizontally into two and three segments; vertically into two and three segments; and both horizontally and vertically into two and three segments. Then they used a “reduce” function to compute all possible segments, which resulted in proper two-dimensional decimations, Blake wrote.
Finally, before beginning an exhaustive search that would utilize combinations of transpositions, the researchers went back and looked again at some of the 650,000 transpositions it had already tested. “Investigating this result further, David used our 9,9,2-vertical segment, 1,2-decimation transposition and AZdecrypt to crib the phrases ‘HOPE YOU ARE,’ ‘TRYING TO CATCH ME,’ and ‘THE GAS CHAMBER,’” Blake wrote. “Eureka! Eventually, the rest of the message came into focus (although not without using additional cryptographic techniques, including the good-old word scramble).
“Essentially all my work on the Z340 was done in Mathematica,” Blake wrote. “I used the Spartan high-performance computing cluster at the University of Melbourne to eliminate candidate transpositions using zkdecrypto and David used AZdecrypt. Otherwise, all the statistical analysis of the Z340 and the creation and analysis of the millions of candidate transpositions was done using Mathematica.
A considerable amount of computational horsepower was required to find the solution to the Zodiac killer’s message, Oranchak told Discover Magazine. That would have made it almost impossible to have used this sort of brute-force approach to decrypt it back in 1969, he said. “They’re just not amenable to this kind of attack,” Oranchak told the magazine.
Content of the Solved Cipher
“Of all the things that stood out was the line ‘that wasn’t me on the TV show’,” Oranchak explained in the video. “At this point I jumped out of my chair because I knew the cipher was received on November 8, 1969, which is about two weeks after someone calling themselves Zodiac called into a TV talk show hosted by Jim Dunbar. This for Oranchak made the solution seem real, as it fit with the events around the time it was received.
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In a letter to the San Francisco Chronicle postmarked April 20, he wrote, "My name is-". The cryptologist Craig P. Bauer proposed the solution "Alfred E. Neuman", the mascot of humor magazine Mad. Ryan Garlick, a University of North Texas computer science and engineering professor, used the key to the Z340 to get the solution "Dr. Eat a Torpedo". Garlick believes that this is an insult directed at D. C. B.
In the same letter, the Zodiac denied responsibility for the fatal bombing of an SFPD police station in Golden Gate Park. He added, "there is more glory to killing a cop than a cid because a cop can shoot back." He also included a diagram of another school bus bomb.