FBI Memo Reveals How the Zodiac Killer's Ciphers Reached the Bureau

# FBI Memo Reveals How the Zodiac Killer's Ciphers Reached the Bureau

By DeClassX

In the summer of 1969, a killer was taunting California. He had already claimed at least five lives and left investigators with almost nothing to work with — no reliable description, no confirmed identity, and no motive beyond what he himself had put to paper. What he had provided, delivered directly to the press, were letters. Cryptic, boastful, and deeply unsettling letters, some of which contained coded ciphers he claimed would reveal his identity if anyone could crack them. A declassified FBI memo dated August 6, 1969, offers a rare bureaucratic window into the moment those materials formally entered the hands of the federal government — and it tells us more about how the investigation functioned than it might first appear.

The memo, originating from the FBI's Sacramento field office and addressed to the Director of the FBI with specific attention to the FBI Laboratory, is a transmittal document. In plain terms, it is a cover letter — the kind of internal paperwork that accompanies physical evidence as it moves through the investigative chain. But in this case, what was being transmitted was extraordinary: the original letters and ciphers sent by the man who called himself the Zodiac.

The Sacramento Special Agent in Charge catalogued four distinct items being forwarded to Washington. The first was an original, undated, three-page letter that began with words that would become chillingly iconic: "Dear Editor, This is the zodiac speaking." The letter ended with a complaint that he "did not get front page coverage" — a line that reveals as much about the Zodiac's psychological profile as any criminal analysis could. He was not simply communicating; he was performing. He wanted attention, and he was angry when he felt he hadn't received enough of it. This letter had been sent anonymously to the San Francisco Examiner, received by that paper, and then turned over to the Vallejo Police Department on August 4, 1969 — just two days before this memo was written.

The remaining three items were photocopies rather than originals: envelopes and letters addressed to the San Francisco Examiner, the San Francisco Chronicle, and the Vallejo Times Herald, each enclosing one of the Zodiac's now-famous ciphers. The decision to send photocopies while retaining or separately handling the originals was standard forensic procedure — preserving the chain of custody for physical evidence while still giving analysts something to work with. The FBI Laboratory in Washington was among the most sophisticated forensic operations in the world at the time, and routing the ciphers there was a logical escalation from local and state-level investigation.

To understand why this memo matters, it helps to know what was happening in California in those weeks. On July 4, 1969 — just over a month before this memo was written — the Zodiac had attacked Darlene Ferrin and Michael Mageau at Blue Rock Springs Park in Vallejo. Ferrin was killed; Mageau survived. Shortly after that attack, an anonymous caller contacted the Vallejo Police Department to take credit for the shooting and reference an earlier double murder at Lake Herman Road. Then, on July 31 and August 1, three California newspapers each received a letter from someone claiming to be the killer, along with one-third of a 408-symbol cipher. The sender threatened to go on a killing spree if the newspapers did not publish their portion of the code on the front page.

The newspapers complied. The full cipher — now known as the Z408 — was assembled and published. Within days, a Salinas schoolteacher named Donald Harden and his wife Betty cracked the first cipher, a solution that revealed a rambling, semi-coherent message about killing humans being "the most thrilling experience" and a strange claim about collecting "slaves" for the afterlife. It did not, despite the Zodiac's promise, reveal his identity.

This memo sits right at the intersection of that public drama and the quieter, procedural world of federal law enforcement. The subject line lists the case under the jurisdiction of the Vallejo Times Herald in Vallejo, California, and classifies it as an extortion matter — a telling legal designation. By threatening violence unless his demands (publication of the ciphers) were met, the Zodiac had triggered federal jurisdiction under extortion statutes. That classification allowed the FBI to formally enter a case that might otherwise have remained solely a local or state matter.

The redactions visible in the memo — standard black bars blocking certain names and identifying information — reflect the FBI's continued application of privacy exemptions even to decades-old documents. These redactions, marked with the codes b6 and b7C and b7D, correspond to categories protecting personal privacy and law enforcement investigative techniques. Whoever was named in those redacted fields — likely the specific agents handling the material, or possibly a source or contact at one of the newspapers — remains protected from public disclosure.

What the memo cannot tell us is whether the FBI Laboratory's analysis of these letters and ciphers yielded anything actionable. The broader historical record suggests that while the Z408 was solved, the three remaining Zodiac ciphers sent over the course of the case were not cracked for decades — the Z340 was only definitively solved in December 2020 by a team of amateur cryptographers, more than fifty years after it was written. The Zodiac's identity has never been officially confirmed.

What this document does tell us is something valuable in its own right: it shows the machinery of a major investigation in motion. Evidence collected at a crime scene, handed off to a local department, forwarded to a field office, and then routed to a federal laboratory — each step documented, logged, indexed. The memo bears a received stamp of August 14, 1969, meaning it took eight days to travel from Sacramento to Washington and be formally logged into the system. Eight days during which the Zodiac was already writing his next letter.

For researchers and true crime historians, documents like this one are essential not because they solve the mystery, but because they map the contours of what was known, when it was known, and how the government responded. The Zodiac case remains open. The ciphers, the letters, and the bureaucratic paper trail that followed them are still being studied. This memo is one small, precise data point in a case that has resisted resolution for more than half a century — and a reminder that even in the age of the federal laboratory and the airmail registered envelope, some questions refuse to be answered.