Arthur Leigh Allen and the Zodiac Case: Forensics, Informants, Outcome

Arthur Leigh Allen is the best-known suspect in the Zodiac Killer case and the only person law enforcement has ever publicly named as a suspect in the investigation.¹ A former Vallejo schoolteacher who lived at his mother’s house and later worked at a hardware store, Allen drew police attention from 1969 onward and accumulated a long list of circumstantial links to the crimes. He was never charged. Fingerprints, palm prints, handwriting analysis, and later DNA testing all failed to tie him to the Zodiac, and he died of a heart attack in August 1992 at age 58.²

Why Police Focused On Him

Allen first came to investigators’ attention in 1969, when police in the Vallejo area questioned him after the local attacks.³ He lived minutes from where Darlene Ferrin was shot on July 4, 1969.¹ After the Lake Berryessa stabbing, officers who spoke with him found bloody knives in his car. Allen said he had been killing a chicken.⁴

The real turn came in 1971. Don Cheney, a former friend, told police that in 1969 Allen had described a plan to shoot out the tires of a school bus and “pick the little darlings off as they come bouncing out.” The phrasing tracked closely with a line from one of the Zodiac’s letters to newspapers, in which the killer talked about shooting out a school bus tire and picking off “the kiddies as they come bouncing out.”² Cheney’s tip pushed Allen to the front of the investigation.

Suspicion sharpened again in the early 1990s. Vallejo Police Captain Roy Conway reopened the case in part on a claim from Ralph Spinelli, a convicted felon facing a potential life sentence, who said Allen had spoken about killing a San Francisco cab driver shortly before the Zodiac killed taxi driver Paul Stine in October 1969. Spinelli offered the information hoping to negotiate a deal, though no deal was made.⁵

On February 14, 1991, police executed a search warrant at Allen’s home on Fresno Street in Vallejo and a boat stored nearby. Officers seized multiple firearms, four pipe bombs, blasting caps, fuses, black powder, hunting knives, ammunition, Zodiac-related news clippings, and a Zodiac Sea Wolf brand wristwatch. As a convicted felon, Allen could have been arrested on the weapons and explosives alone, but no charges were filed, and nothing recovered directly connected him to the murders.⁶

The Circumstantial Case

Investigators and journalists assembled a striking set of coincidences over the years. Allen wore a Zodiac Sea Wolf watch that carried the same crosshair symbol the killer used as his signature.¹³ An associate told police Allen had talked about killing people and about attaching a flashlight to a gun barrel, a method attributed to the Zodiac. He was ambidextrous, which some theorists suggested could help disguise handwriting.

A Royal typewriter matching the type used to produce confession letters linked to the 1966 murder of Cheri Jo Bates in Riverside was also found in his home.⁴ In 1991, Michael Mageau, who survived being shot in the Zodiac’s July 1969 attack at Blue Rock Springs Park, identified a photograph of Allen as the man who shot him.³

There was also a timing coincidence people have long pointed to. In the early 1970s Allen was arrested for child molestation and sentenced to four years at Atascadero State Hospital, and the Zodiac’s killings and taunting letters stopped during that period of institutionalization.⁷

What the Forensic Tests Showed

Every major forensic comparison ran against him. His fingerprints did not match prints recovered from Paul Stine’s taxicab, and his palm print did not match one found on a Zodiac letter.³

Handwriting was just as unhelpful for the prosecution theory. Every examiner who compared Allen’s writing to the Zodiac letters concluded he was not the writer. Samples were obtained from both his left and right hands, and both openly and without his knowledge. Sherwood Morrill, the documents examiner who worked the case from the beginning, maintained until his death that the Zodiac had used his own natural handwriting in the letters, a conclusion that pointed away from Allen.⁵ Allen also did not match witness descriptions of the killer’s appearance.³

The first police search of Allen’s trailer, conducted in 1972 by San Francisco Police Department Homicide Inspectors Bill Armstrong and Dave Toschi, turned up nothing tying him to the case, and fingerprint and handwriting comparisons at that time also failed to produce a match. Police largely lost interest until Spinelli’s claim revived the case two decades later.⁶⁵

Allen himself sat for a polygraph during the 1970s in a session he described as lasting ten hours. The results indicated he was truthful when he denied involvement in the Zodiac murders. According to Allen, police dismissed the result by telling him he was “a sociopath” who could cheat on lie detector tests.⁸

DNA closed one more door. In 2002, a decade after Allen’s death, SFPD homicide detectives tested saliva from envelopes of letters attributed to the Zodiac. Inspector Kelly Carroll reported that a partial profile developed from that material did not match Allen.²⁹ Some researchers have questioned whether the DNA on the envelopes necessarily came from the Zodiac himself.¹⁰

Problems With the Informants

Much of what made Allen look like the Zodiac came from two informants, and the reliability of both has been called into question.

Don Cheney’s account grew over the years. His stories incorporated details that appeared to come from later media coverage and from Robert Graysmith’s book, including the Zodiac wristwatch, which he added to his narrative years after his initial police interview. By 2006 Cheney was claiming that Allen had taken him to a crime scene and confessed to being a contract killer. His 1991 polygraph was inconclusive, though a second test was reportedly positive. Allen’s brother and sister-in-law believed Cheney had invented his stories in retaliation for an alleged molestation incident involving Cheney’s daughter, and retired detective George Bawart also came to doubt Cheney’s honesty, going so far as to suggest Cheney himself might have been involved in the crimes.⁵

Ralph Spinelli was a convicted felon offering information while trying to avoid a life sentence. Captain Conway eventually stopped believing Allen was responsible for the Paul Stine murder after fingerprint evidence excluded him.⁵

Death and Public Naming

Allen died of a heart attack on August 26, 1992. He was 58. In 1992, Vallejo police had still been pressing him to take another polygraph, and he had reportedly drafted terms for the test on his home computer, hoping a passing result would clear his name. He died before the examination could take place.⁸ Authorities acknowledged they had never been able to build a strong enough case to arrest him.²

Allen’s status as the prime suspect reached the public mainly through Robert Graysmith, a former editorial cartoonist at the San Francisco Chronicle. In his 1986 book Zodiac, Graysmith identified Allen as the likeliest suspect but used the pseudonym “Richard Starr,” hoping publication would draw out conclusive evidence. After Allen’s death, Graysmith’s 2002 Zodiac Unmasked named him directly and described him as “a terrifying sociopath and convicted pedophile whom police long considered the prime suspect.”¹¹ David Fincher’s 2007 film Zodiac, based on Graysmith’s books, brought the case and Allen’s name to a much wider audience.

In October 2024, Netflix released the three-part docuseries This Is the Zodiac Speaking, focused on Allen.¹² The series follows the Seawater siblings — David, Connie, and Don — whose mother, Phyllis Seawater, was close to Allen throughout their childhood. The siblings say Allen took them on trips in the 1960s during which they now believe he committed nearby murders. David Seawater says Allen called him sobbing in 1992, shortly before his death, and confessed to being the Zodiac. Connie says she asked Allen on a 1991 sailing trip whether he was the Zodiac, and he told her that if he answered, he would have to kill her.¹³

After their mother’s death in 2017, the siblings found a box of letters Allen had written to her. In one, he wrote that “the most dangerous thing is when I almost decided to confess.” Another said that seeing murder headlines made his “palms sweaty.”¹³ The producers described the material as evidence law enforcement had not previously reviewed.¹²

Where the Case Stands

The Zodiac case remains officially open. The Vallejo Police Department still considers Allen a suspect but continues to investigate other theories and individuals, and has submitted Zodiac envelopes for additional DNA testing. Earlier efforts produced only partial profiles insufficient for forensic genealogy or a definitive identification.¹⁰

Other suspects have been proposed over the decades, including Lawrence Kane, Ross Sullivan, Richard Gaikowski, and Earl Van Best Jr.³ Investigators have acknowledged that the killer could also be someone who has never appeared on any suspect list. Allen sits where he has sat for more than fifty years: the man police suspected the most, investigated the longest, and never managed to charge.

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