Thousands of men have been named as a possible suspect for the Zodiac Killer, an unidentified serial killer active between December1968 and October1969. The Zodiac murdered five known victims in the San Francisco Bay Area, operating in rural, urban, and suburban settings. His known victims were three young couples and a lone male cab driver, while he claimed in letters to have murdered thirty-seven people. The case has been described as "arguably the most famous unsolved murder case in American history", and has become a fixture of popular culture and focus for amateur detectives.

In 2012, The Guardian wrote that over 2,500people have been brought up as a possible Zodiac suspect, and at least a half-dozen names were credible. The San Francisco Police Department (SFPD) had investigated an estimated 2,500suspects by 2009. Richard Grinell, who runs the website Zodiac Ciphers, said in 2022 that "there are probably 50 or 100suspects named every year".

While many theories regarding the identity of the Zodiac have been suggested, the only suspect authorities ever publicly named was Arthur Leigh Allen, a former elementary school teacher and convicted sex offender who died in 1992. No one was ever arrested for the crimes. Despite continued efforts into the 21stcentury, the killer's identity is unknown.

Background The Zodiac Killer claimed in messages to newspapers to have committed thirty-seven murders. Investigators agree on seven confirmed assault victims, all in Northern California, of whom five died and two survived:

David Arthur Faraday and Betty Lou Jensen were shot and killed on December20, 1968, on Lake Herman Road in Benicia. Michael Renault Mageau and Darlene Elizabeth Ferrin were shot around midnight between July4 and5, 1969, in the parking lot of Blue Rock Springs Park in Vallejo. Mageau survived the attack; Ferrin was later pronounced dead. Bryan Calvin Hartnell and Cecelia Ann Shepard were stabbed on September27, 1969, at Lake Berryessa in Napa County. Hartnell survived, but Shepard died as a result of her injuries on September29. Paul Lee Stine was shot and killed on October11, 1969, in the Presidio Heights neighborhood of San Francisco.

The Zodiac coined his name in a series of taunting messages that he mailed to regional newspapers, threatening killing sprees and bombings if they were not printed. He also said that he was collecting his victims as slaves for the afterlife. Some letters included cryptograms or ciphers; of the four codes he produced, two remain unsolved while the others were cracked in 1969 and 2020. The last confirmed Zodiac letter was sent in 1974, in which he claimed to have killed thirty-seven victims. He had said earlier that many of them were in Southern California, including Cheri Jo Bates, who was murdered in Riverside in 1966; a connection between the two has not been proven.

Arthur Leigh Allen

Arthur Leigh Allen was a former elementary school teacher and convicted child molester. He remains the only publicly named suspect by the police. Several of his friends have claimed that he had called himself The Zodiac, that he liked to shoot young couples in lover's lanes, and that he had aspirations to write a book about a serial killer named The Zodiac. Additionally, the timing of his imprisonment aligns with the Zodiac's known correspondence with the police. By far the lead most pursued by the police, he was the subject of several searches but was never arrested. His fingerprints and handwriting could not be definitively linked to the Zodiac. He died in August1992.

In the early 2000s, a partial DNA profile possibly belonging to the Zodiac was obtained and Allen's DNA did not match. True crime author Robert Graysmith wrote two books in 1986 and 2002, in which Allen's culpability was strongly suggested. Zodiac, a 2007 film based on Graysmith's books, portrayed Allen as the likely killer.

Earl Van BestJr. In 2014, Gary Stewart and Susan Mustafa published a book, The Most-Dangerous Animal of All: Searching for My Father... And Finding the Zodiac Killer, in which Stewart claimed his search for his biological father, Earl Van BestJr., led him to conclude Van Best was the Zodiac. Stewart based his hypothesis on circumstantial evidence, including a composite sketch resembling Van Best, partial fingerprint and handwriting matches, encrypted messages in Zodiac letters, and partial DNA connections.

In 2020, the book was adapted for FX Network as a documentary series. To validate Stewart's claims, the producers enlisted private investigator Zach Fechheimer, who uncovered that Stewart had manipulated a police report and traced Van Best to being present in Europe during the Zodiac's known activities. Additionally, experts discredited the DNA analysis and the handwriting and fingerprint matches. The producers chose to withhold their findings until near the end of the documentary's production to minimize their impact on both the series and Stewart. Six months after production, director Kief Davidson stated that he thought Stewart's father was not the Zodiac, while executive producer Ross Dinerstein remained uncertain about Van Best's potential involvement. Van Best died in 1984.

Giuseppe Bevilacqua In 2017, Italian journalist Francesco Amicone conducted an investigation that implicated Giuseppe "Joe" Bevilacqua, a retired U.S.Army sergeant and former superintendent of the Florence American Cemetery and Memorial, as a suspect in both the Zodiac and Monster of Florence () cases. Bevilacqua had previously testified at the trial of suspect Pietro Pacciani in 1994.

Starting in May 2017, Bevilacqua and Amicone began having multiple meetings; according to Amicone, Bevilacqua implied his responsibility for both cases in phone correspondence. Bevilacqua agreed with Amicone's request to turn himself in but later changed his mind. Citing professional ethics reasons, Amicone did not record the conversation. Amicone's inquiry was published in multiple Italian newspapers, and has been continued since then on his blog. Italian authorities dismissed their investigation into Bevilacqua in 2021. He died on December 23, 2022. Amicone claimed a DNA profile was sent to U.S. authorities investigating the Zodiac case in November 2023.

Paul Doerr Jarrett Kobek's 2022 book How to Find Zodiac named Paul Doerr, who died in 2007, as a suspect. Doerr was a North Bay resident with a post office box in Vallejo, where the first murders took place. Born in 1927, Doerr's age in 1969 (42) as well as his height (5'9") would have been consistent with witness estimates.

Doerr was an avid fanzine publisher and letter-writer throughout the 1960s and 1970s, and many of his writings exhibit circumstantial parallels with the Zodiac. Paul Haynes, a researcher for the true crime book I'll Be Gone in the Dark, called Doerr "the best Zodiac suspect that's ever surfaced." Doerr's daughter read Kobek's book with the intent of suing the author for libel, but came away impressed with his research, adding in interviews that her father had at times been violent and abusive. Kobek sent a nineteen-page document to the SFPD's Major Crimes Division regarding the similarities; he did not receive a response.

Doerr was a member of the Minutemen, a right-wing militant group that sent out threatening letters to supposed communists using a symbol that resembled the Zodiac's. Some of the Zodiac attacks took place at hangout spots of Doerr's daughter. In his fanzine Pioneer, Doerr references the same formula for an ANFO bomb later given by the Zodiac, which Kobek argues was not widely known before the Internet and the publication of The Anarchist Cookbook in 1971. Doerr hinted in a 1974 letter to the neopagan magazine Green Egg that he had previously killed people; Kobek writes that that part of the letter was not intended for publication, but Green Egg had a policy of publishing every letter in full.

Doerr was interested in cryptography; in issue#1 of his J. R. R. Tolkien fanzine Hobbitalia, he published a cipher in Cirth. This came three days after Zodiac sent the "Z13" cipher, and Kobek argues that the solution to the Hobbitalia cipher is one of only three possible solutions to Z13. In Hobbitalia#2, Doerr praised the Society for Creative Anachronism, a group of medieval cosplayers, which could explain the executioner-style costume used at Lake Berryessa. A Renaissance Faire took place nearby on the day of the attack, and there is an undated photo that shows Doerr carrying a knife similar to the one described in the Lake Berryessa attack. Doerr also made a list of books he wanted to sell, including E.Royston Pike's The Strange Ways of Man, which in one passage describes headhunters killing victims so they could have slaves in the afterlife. In a letter to a different fanzine in 1970, Doerr advocated using solely 1¢stamps to spite the United States Postal Service, a practice the Zodiac employed on some of his letters.

Richard Gaikowski

In the 1980s, a former co-worker of Richard Gaikowski nicknamed "Goldcatcher" (also known as Blaine Blaine) wrote long letters to law enforcement accusing him of being the Zodiac Killer. Gaikowski was later investigated by Napa County detective Ken Narlow. He had told Narlow that he was not in the United States at the time of the Lake Herman Road murders, but was unable to prove this as he had lost his passport.

According to Zodiac researcher Tom Voigt, who has Gaikowski as his number one suspect, the FBI investigated Gaikowski but dismissed him as a suspect upon hearing the claim he had been out of the country, despite allegedly losing the passport. San Francisco and Napa police have declined to compare DNA samples of Gaikowski and the Zodiac.

Gaikowski had moved to the Bay Area in 1963. At the time of the Zodiac murders, he was a reporter and editor for the counterculture tabloids Good Times and the Martinez Morning News Gazette. Gaikowski's appearance resembled the Stine composite sketch, and the word "Gyke" also appears in the Zodiac cipher that claimed to contain his identity. When he was working for the Gazette, Gaikowski was minutes away from two Zodiac murder scenes.

Gaikowski was trained as a medic in the army, and the taxicab driver Paul Stine had a piece of his shirt torn off by the Zodiac; this was a common practice taught to medical personnel. Paul Stine's sister told Voigt she recognized Gaikowski at Stine's funeral. This would also match with the claim that Ferrin's attacker and boyfriend were named Richard. Wednesdays were the busiest day for the Good Times, and the Zodiac never mailed a communication on that day of the week. In 1971, Gaikowski was involuntarily committed to Napa State Mental Hospital and diagnosed with a mental illness, and the Zodiac stopped writing letters during this time; Gaikowski was released in late 1973. He later operated a movie theater, and died in 2004.

In 2009, an episode of the History Channel television series MysteryQuest investigated Gaikowski, and Goldcatcher made an appearance in disguise, along with Voigt. On the episode, Goldcatcher provided recordings of Gaikowski's voice. Nancy Slover, the Vallejo police dispatcher who was contacted by the Zodiac shortly after the Blue Rock Springs attack, identified a recording of Gaikowski's voice as being the same as the Zodiac's. However, the History Channel referred to Goldcatcher as a "conspiracy theorist with low credibility", and a San Francisco police dispatcher referred to him as "one of the top three Zodiac kooks."

Lawrence Kane