The Zodiac coined his name in a series of taunting messages that he mailed to regional newspapers, in which he threatened killing sprees and bombings if they were not printed.

Despite many theories about the Zodiac's identity, the only suspect authorities ever named was Arthur Leigh Allen, a former elementary school teacher and convicted sex offender who died in 1992.

The case also remains open in the California Department of Justice, Federal Bureau of Investigation, the city of Vallejo, as well as in Napa and Solano counties.

Five victims were killed during these attacks, and two survived:[2] From 1969 to 1974, the Zodiac mailed heavily misspelled letters and ciphers to law enforcement and media outlets.

Authors Michael Kelleher and David Van Nuys speculated that the seven months between the attacks on Lake Herman Road and at Blue Rock Springs was a "cooling off period" for the Zodiac.

[11]: 31  Kelleher and Nuys suggest that Ferrin would not tell Mageau to ignore the mystery driver, nor would they assume he was a police officer, if they had not stopped at the spot by choice.

[20] At 4:00 p.m. on September 27, 1969, Pacific Union College students Bryan Hartnell (20) and Cecelia Shepard (22) were picnicking at Lake Berryessa on a small island connected by a sand spit to Twin Oak Ridge.

The killer drew the symbol on Hartnell's car door with a black felt-tip pen and wrote beneath it:Vallejo 12-20-68 7-4-69 Sept 27–69–6:30 by knife[25] After hearing the victims' screams, a fisherman and his son sought help.

[11]: 63f  Since they had potentially seen the Zodiac without his hood, the women worked with Napa Valley Register photographer Robert McKenzie to create a composite sketch using an Identi-Kit.

Around 9:40 p.m. on October 11 in downtown San Francisco, the Zodiac hailed a cab which was driven by a doctoral student named Paul Stine.

The cryptology group included American software engineer David Oranchak, Australian mathematician Sam Blake and Belgian programmer Jarl Van Eycke.

[42][43] In the decrypted message, the Zodiac denied being the "Sam" who spoke on A.M. San Francisco and explained he was not afraid of the gas chamber "because it will send me to paradice all the sooner."

The team submitted their findings to the FBI's Cryptographic and Racketeering Records Unit, which verified the decryption and concluded the decoded message gave no further clues to the Zodiac's identity.

[57] Shortly after the "Halloween Card", Avery also received an anonymous letter about the parallels between the 1966 murder of Cheri Jo Bates and the Zodiac.

[2] The Chronicle received a letter postmarked February 14, 1974, explaining that the Symbionese Liberation Army's initials spelled out an Old Norse word meaning "kill."

[67] In 2019, the unsolved murder was connected to the Zodiac when Kristi Hawthorne, the Director of the Oceanside Historical Society, was researching St. Malo for another project.

[70] Two days later on June 4, Robert George Domingos (18) and his fiancée Linda Faye Edwards (17) were shot dead on a beach in Gaviota State Park, just west of Tajiguas.

[70] In a 1972 press conference, Santa Barbara County Sheriff John Carpenter stated "there now appears to be a high degree of probability" that the Zodiac committed the 1963 murders.

"[76][74] A classmate of the slain teenagers who grew up to be a clinical psychologist and police officer said in 2011, "I believe the murders were the work of the Zodiac killer, but I can’t prove it.

Police investigated a 51-year-old man living in a beach shack, a teenager alleged by a priest to be violent, and a 19-year-old Marine from San Diego who killed his parents and sister in Illinois.

[79] Both the Ocean Beach and Lake Herman Road murders used a .22 Remington Arms Model 550-1 rifle, but the ballistics did not match between the cartridges found at the two scenes.

[68] On October 30, 1966, Cheri Jo Bates, an 18-year-old student at Riverside City College (RCC), spent the evening at the campus library annex until it closed at 9:00 p.m.

During the 1970 investigation, Sherwood Morrill, California's top "questioned documents" examiner, expressed his opinion that the poem was written by the Zodiac.

Police across multiple jurisdictions made a tentative connection between a single culprit and at least a dozen unsolved homicides that occurred between the late 1960s and early '70s.

The Zodiac had warned he would vary his modus operandi in a previous letter, "when I comitt my murders, they shall look like routine robberies, killings of anger, + a few fake accidents, etc.

"[10] The only man ever named by the police as a suspect is Arthur Leigh Allen, a former elementary school teacher and convicted sex offender who died in 1992.

In Zodiac, Graysmith refers to Arthur Leigh Allen as "Robert Hall Starr" to protect his identity and avoid litigation.

The audience were given a survey with the prompt, "I think the Zodiac kills because..." They were asked to complete the sentence and promised the best response would be rewarded with a Kawasaki motorcycle.

Hanson hoped the killer's supposed egotism would lure him to the movie, and deployed volunteers to detain anyone whose handwriting matched the Zodiac's.

[128] The Zodiac has inspired villains in multiple movies, including Scorpio in Dirty Harry (1971), the Gemini Killer in The Exorcist III (1990), John Doe in Seven (1995), and the Riddler in The Batman (2022).