The Zodiac Killer: The Code Breakers Pt. 3

December 11, 2020. The world is nine months into a pandemic. A software developer in Virginia gets on a video call with a mathematician in Melbourne and a programmer in Belgium. Three people, three countries, three time zones, and on the screen between them sits a 340-character cipher that the FBI, the codebreaking community, and fifty-one years of obsessives had all failed to crack. By the end of the call, for the first time since 1969, it begins to speak.

This week on Mugshot Mysteries, Kathryn and Gabriel continue their four-part Zodiac series with Part 3, "The Code Breakers," the episode about the writing, the ciphers, and the people the case quietly destroyed.

We start by laying out the complete authenticated record, every confirmed Zodiac communication in order, because the letters are the case. The three coordinated newspaper letters of July 1969 and the first cipher. The bloody swatch of Paul Stine's shirt mailed to the Chronicle. The school-bus threat that put armed officers on Bay Area buses for weeks. The plea to attorney Melvin Belli. The demand that the public wear his crossed-circle buttons, and the violence he claimed when they would not. The Halloween card to reporter Paul Avery. And the final confirmed letter in 1974, praising The Exorcist, after which he simply went silent.

Then we go deep on the Z340. We explain why it defeated everyone for half a century: it was not just a substitution cipher but a transposition too, the characters read diagonally across a grid, a complexity researchers believe the Zodiac may have created partly by accident. We walk through how David Oranchak, Sam Blake, and Jarl Van Eycke finally broke it, what it actually said, which was more taunting and not a name, and how the FBI confirmed the most famous cipher solve in American history by email. Then the two that remain open: the thirteen-character Z13, prefaced "My name is," too short to ever prove a solution, and the Z32 with its Mount Diablo map.

And we close on the human cost. The jurisdictional disaster across four agencies with no shared database. Detective Dave Toschi, the bow-tie-wearing, animal-cracker-carrying inspiration for both Bullitt and Dirty Harry, who filled eight filing cabinets on one case and was pulled from it after he was caught writing anonymous fan mail about himself. And cartoonist Robert Graysmith, whose obsession produced the book that shaped public understanding of the case and cost him his marriage. The Zodiac did not have to do anything to these men. He just had to stay unsolved.

Part 4, the finale and the names, is next.

This is Part 3 of our four-part Zodiac series. New episodes drop every Mugshot Monday. Search Mugshot Mysteries wherever you listen.

SOURCES:

Case records and reporting on the Zodiac investigation across the San Francisco Police Department, the Vallejo Police Department, the Napa County Sheriff's Office, the Solano County Sheriff's Office, and the FBI; the authenticated archive of Zodiac letters, cards, and ciphers held by the San Francisco Chronicle, the San Francisco Examiner, and the Vallejo Times-Herald, 1969 to 1974; the 1969 solution of the 408-character cipher by Donald and Bettye Harden of Salinas; the December 2020 solution of the 340-character cipher (Z340) by David Oranchak, Sam Blake, and Jarl Van Eycke using the AZdecrypt tool, confirmed by the FBI, and Oranchak's documentation of the solution and its diagonal transposition structure; the 2024 proposed Z13 and Z32 solutions published by Fayçal Ziraoui, unconfirmed by law enforcement; Graysmith, R., Zodiac, 1986, and Zodiac Unmasked, 2002; reporting on Detective Dave Toschi, including his role as the inspiration for the films Bullitt (1968) and Dirty Harry (1971) and his 1978 removal from the investigation after the discovery of self-authored letters; reporting on Chronicle reporter Paul Avery and the 1970 Halloween card; suspect background on Arthur Leigh Allen and Lawrence Kane; reporting on the partial DNA profile developed from the Zodiac correspondence and the limits of CODIS and genetic genealogy in this case, including comparison to the 2018 genetic-genealogy identification of the Golden State Killer; Fincher, D., Zodiac, 2007; and the 2025 SXSW documentary The Zodiac Killer Project.

DISCLAIMER:

Content warning: This episode discusses multiple homicides, threats of mass violence against children, and graphic crime detail. Please take care while listening, and consider stepping away if any of this is difficult. Nothing in this episode constitutes legal advice.

The Mugshot Mysteries podcast is independently produced and is not affiliated with, sponsored by, or endorsed by any individual, agency, author, publisher, or production referenced in this episode, including any law enforcement agency, the FBI, the San Francisco Chronicle, or any film or documentary named.

The Zodiac case is officially unsolved, and no person has ever been charged or convicted. Individuals named in this episode in connection with the investigation, including Arthur Leigh Allen and Lawrence Kane, are identified solely in the context of publicly reported investigations and theories, not as a finding of guilt, and both are deceased. Nothing here should be read as an accusation that any living person committed any crime.

The 2020 solution of the Z340 cipher was confirmed by the FBI. The proposed solutions of the shorter Z13 and Z32 ciphers, including those advanced by Fayçal Ziraoui and others, have not been confirmed by law enforcement and remain disputed; because the Z13 is only thirteen characters long, multiple conflicting solutions can be produced and none can be definitively proven. We present these as claims and interpretations, not as established fact. Our account is drawn from publicly available sources including law enforcement records, the authenticated letter archive, the published work of the cipher researchers, books, and journalism, and details vary across sources.

Characterizations of Detective Dave Toschi, Robert Graysmith, Paul Avery, and others reflect documented reporting and the hosts' interpretation, and are not statements of established fact about any person's private life or state of mind. References to any person, living or deceased, are made in the context of documented history and public records and are not intended to defame, harass, or cause harm. The commentary and interpretations offered by the hosts are their own opinions and do not constitute statements of established fact or legal conclusions. Any third-party names and trademarks remain the property of their respective owners and are referenced under fair use for purposes of commentary, criticism, and reporting. Nothing in this episode constitutes legal advice.