FBI Lab Request Hints at Zodiac Cipher Break in 1969

# FBI Lab Request Hints at Zodiac Cipher Break in 1969

In the summer of 1969, the San Francisco Bay Area was gripped by fear. A killer who called himself the Zodiac had already claimed multiple victims and was taunting law enforcement with encrypted letters mailed to regional newspapers. Police agencies were flooded with tips, theories, and leads — most of them dead ends. But one piece of correspondence, postmarked San Francisco on August 10, 1969, was unusual enough that it traveled from a Vallejo police sergeant's desk all the way to the FBI Laboratory in Washington, D.C. A newly declassified memo dated August 14, 1969, tells that story.

The document is a standard FBI routing form — designated FD-36, the bureau's internal transmittal sheet for field communications — sent via airtel with airmail registered priority from the Special Agent in Charge (SAC) in Sacramento to the FBI Director's office, attention the FBI Laboratory. The subject line identifies the case as an extortion matter, with the Vallejo Times-Herald listed as the victim and the perpetrator designated simply as "Unknown Subject," the bureau's standard placeholder for an unidentified suspect. The case number, 9-68, and a reference to a prior Sacramento airtel dated August 6, 1969, confirm this was not an isolated communication but part of an active, ongoing federal investigation threading together multiple California law enforcement jurisdictions.

What makes this memo worth examining carefully is what it describes enclosing: a 3-by-5 index card bearing a typewritten note addressed to a named — but now redacted — Vallejo Police Department sergeant, signed off with the phrase "concerned citizen." Along with that card came a physical object described simply as a "key." The anonymous letter writer, whoever they were, claimed this key would, in their words, "prove to be beneficial to you in connection with the cipher letter writer." That phrase is the crux of everything. The cipher letter writer, in the context of August 1969 Vallejo, California, means one person: the Zodiac Killer.

To understand why this matters, a brief timeline is necessary. On July 31, 1969, the Zodiac mailed three identical cipher letters — each containing roughly one-third of a 408-symbol cryptogram — to the San Francisco Chronicle, the San Francisco Examiner, and the Vallejo Times-Herald. He demanded the papers print the ciphers on their front pages or, he threatened, he would "cruse" [sic] around all weekend killing lone people. The papers complied. The full 408-cipher, assembled from all three letters, was solved on August 8, 1969, by a Salinas schoolteacher named Donald Harden and his wife Bettye — though Zodiac disputed the solution's completeness. A second cipher, the infamous 340-character cryptogram, would follow in November and would remain unsolved for over fifty years.

The memo's reference to "the cipher enclosed with referenced airtel" — the August 6 Sacramento communication — places this anonymous tip squarely in the immediate aftermath of that frenzied first cipher event. Someone, somewhere in or around San Francisco, had seen the coverage, perhaps the Vallejo Times-Herald's front-page printing of the cipher, and believed they had information that could help crack the code or identify the writer. They chose to remain anonymous, signing only as a "concerned citizen," and they mailed their note from San Francisco on August 10 — just two days after the Hardens submitted their solution to the FBI.

The FBI's response was methodical and professional. The Sacramento field office requested that both the envelope and its contents — the 3-by-5 card and the mysterious key — be examined for latent fingerprints. The memo is careful to hedge its language regarding the key's significance, noting it "may or may not have some bearing upon the solution of the cipher." This is the cautious, measured language of investigators who have learned not to read too much into unsolicited tips, particularly in a high-profile case already generating enormous public interest. The instruction that items should be returned to the San Francisco field office upon completion, for eventual return to the Vallejo Police Department, suggests the original evidence chain was being carefully preserved.

A handwritten notation at the bottom of the document — "COPY AND SPECIMENS RETAINED IN LAB" — confirms the FBI Laboratory did process the materials. What they found, if anything, is not recorded on this page. The names of the Vallejo sergeant addressed in the letter and the laboratory personnel referenced are redacted under exemption b7c, which protects the identities of law enforcement personnel in investigative files. Two partially legible names appear in the document's lower margin — McEvery and Tilles — possibly Sacramento field office personnel involved in processing the memo, though their precise roles are unclear from the document alone.

What this single page illuminates is the sheer volume of material the Zodiac investigation was generating in real time. Within days of the first cipher's publication, an anonymous member of the public had already mailed a physical "key" to law enforcement. The FBI was routing physical evidence across California, coordinating between its Sacramento and San Francisco field offices and the Vallejo Police Department, while simultaneously processing forensic submissions through its central laboratory. The extortion framing of the case — referencing the Vallejo Times-Herald as victim — reflects the legal theory under which federal jurisdiction was established, since the Zodiac's threats against the newspapers constituted a federal extortion offense, giving the FBI its entry point into what was otherwise a California homicide investigation.

The open question this document leaves behind is tantalizing: what was the key? The word is used without elaboration — it could mean a literal physical key, a decoder sheet, an alphabetic substitution table, or something else entirely. The memo does not say, and no accompanying document in this release clarifies the matter. Whether the anonymous tip from a "concerned citizen" led anywhere, whether the fingerprint examination produced any usable results, and whether the key bore any relationship to the Zodiac's encryption methods — all of that remains, like so much of this case, officially unresolved.

For researchers digging through the Zodiac files, this memo is a reminder that the investigative record is vast, fragmented, and still yielding surprises. Somewhere in the archive, the answer to what that key was may still be waiting.

— DeClassX