On March 13, 1971, a letter attributed to the Zodiac Killer arrived at a Northern California newspaper, asserting responsibility for an additional killing. The Zodiac — an unidentified, self-styled murderer who terrorized the San Francisco Bay Area beginning in 1968 — communicated intermittently through letters, ciphers and phone calls. Each letter prompted intense media attention and police scrutiny; many claimed victims or admissions of crimes beyond the confirmed attacks. Context and content The Zodiac’s confirmed attacks, widely attributed to the period from late 1968 to 1969, included the murders of David Faraday and Betty Lou Jensen (December 1968), Darlene Ferrin and Michael Mageau (July 1969; Mageau survived), and the killing of Paul Stine (October 1969) in San Francisco. The author of the March 13, 1971 letter claimed another victim, a common pattern in Zodiac correspondence where the writer sought to enlarge their notoriety or to taunt investigators. Specific details in the 1971 note varied between reports; some newspapers printed excerpts while law-enforcement files later described it as one of several communications whose provenance was disputed. Investigative response and authenticity questions Law-enforcement agencies tracked all Zodiac letters for forensic and linguistic evidence, but authentication was often difficult. Handwriting analysis, postage and postmark tracing, paper and ink comparisons, and coded messages were used to evaluate claims. In many cases, police and independent researchers concluded that at least some letters purportedly from the Zodiac were hoaxes. The 1971 letter’s claim of a new victim was treated with caution; investigators sought corroborating evidence such as matching ballistics, medical reports, or missing-persons cases that fit the timeline and modus operandi. Publicly available records do not show a confirmed, new Zodiac victim directly linked to that specific letter. Impact on public perception and media Letters like the March 13, 1971 note fed public fear and curiosity and influenced how newspapers and television covered the case. Sensational and speculative reporting sometimes conflated unverified claims with established facts, complicating later historical assessment. At the same time, widespread publication of letters and cipher material spurred civilian researchers to analyze texts, offering leads but also generating false trails. Ongoing historical and forensic relevance Decades after the Zodiac communications, researchers and some law-enforcement teams have reexamined letters using modern forensic techniques, including DNA analysis from stamps and envelopes and computerized handwriting comparison. While these advances have clarified some aspects of certain letters, many communications remain inconclusively attributed. The March 13, 1971 letter is part of that body of contested material: it is documented in contemporary press accounts and investigator files but not conclusively proven to describe a verifiable, additional Zodiac homicide. What is certain and what is disputed It is historically verifiable that a letter claiming responsibility for another killing was received on or about March 13, 1971, and that newspapers reported its contents. What remains disputed is whether the letter was genuinely authored by the Zodiac and whether the claimed murder can be definitively connected to the Zodiac’s confirmed crimes. Researchers must therefore distinguish between the documented existence of the letter and the unresolved questions about its authenticity and the factual accuracy of its claims. Why this matters The Zodiac case remains significant both for its human toll and for its influence on criminal investigation, media coverage of serial crimes, and public fascination with unsolved mysteries. Letters like the March 13, 1971 communication demonstrate how claims can shape investigation and public memory even when they cannot be fully authenticated, and they underscore the continuing challenges of separating provable fact from assertion in long-unsolved cases.