On January 13, 1974, a letter purporting to be from the unidentified serial offender known as the Zodiac Killer arrived at newspapers serving the San Francisco Bay Area. The Zodiac first gained wide public attention in 1969 after a series of murders in northern California and a pattern of letters and cryptograms sent to newspapers and law enforcement. Over the following years the correspondence—sometimes threatening, sometimes boastful, sometimes containing ciphers—became a defining and unsettling element of the case. By 1974 the Zodiac case had already become a prolonged media and police investigation. Investigators had linked several murders and attacks in the late 1960s and early 1970s to a single writer through handwriting, content, and claims of responsibility, though not all scholars and law-enforcement officials agreed on which crimes were attributable to the same individual. The letters often demanded publication in specific newspapers and included details that the sender claimed only the perpetrator would know; at times they also contained puzzles or ciphers, some of which were later solved, others remaining undeciphered or disputed in attribution. The January 13 letter fits into this pattern of continued, intermittent communication. Like prior mailings, it was routed to major Bay Area news outlets and prompted renewed public attention and police review. Authorities typically treated such writings as potential evidence—examining postmarks, paper, envelopes, handwriting, and linguistic content for links to known letters and for forensic leads. Newspapers published select excerpts at law-enforcement request or to maintain public awareness about the dangers to the community. The impact of these mailed communications extended beyond immediate investigative uses. The letters shaped public perception, intensified media coverage, and complicated the work of multiple law-enforcement agencies as they balanced investigative priorities with managing public fear. Over time the Zodiac correspondence became central to discussions about the case: which messages were authentic, which were hoaxes, and what the claims within them revealed about the sender’s identity and motives. Decades later, the Zodiac case remains officially unsolved, and researchers, journalists, and amateur investigators continue to examine the corpus of letters and associated evidence. Some later analyses have argued for reexamination of forensic material with modern techniques; others caution that attribution of any single letter to the Zodiac should be treated carefully when documentary or forensic linkage is weak. The January 13, 1974 mailing is therefore part of a larger, complex record—valuable to historians of crime and true-crime researchers but also subject to ongoing debate about authenticity and interpretation. Because the case involves unresolved crimes and contested evidence, contemporary accounts and retrospectives emphasize what is documented—dates of mailings, the circulation of specific texts, and investigative responses—while noting where attribution or interpretation remains uncertain. The January 1974 letter is one entry in that documented sequence of communications that sustained public attention and investigative effort long after the initial crimes in the late 1960s.