Allen signed his letters with the same symbol the Zodiac did.
The Zodiac killer is an unknown murderer who terrorized northern California in the 1960s and 1970s, primarily targeting couples parked at lovers’ lanes. He communicated regularly with the police and media, sometimes through cyphers. One of the main suspects police liked for the Zodiac was a veteran former school teacher who was fired after he was caught molesting children. The man, Arthur Leigh Allen, was considered by many to be the prime suspect in this unsolved case. This theory was advanced by Robert Graysmith, a former political cartoonist for the San Francisco Chronicle at the time of the murders who went on to write the book Zodiac: The Shocking True Story of the Hunt for the Nation’s Most Elusive Serial Killer in 1986.
[*] John Douglas, the FBI profiler Mindhunter is based on says that many serial killers wish to be in the armed forces and serve as police officers, but lack the social skills to succeed in those jobs. Arthur Leigh Allen served in the navy but was dishonourably discharged in 1958 for an undisclosed reason.
[*] Another common trait of serial killers is animal abuse. This is one of three characteristics in the Macdonald triad, which is a predictor of a future violent serial offender. Allen’s sister-in-law, Karen Allen, has said that Allen mutilated animals as a child.
[*] In 1974 he was fired from his job as a school teacher after he was caught molesting students. He was convicted and spent 3 years in prison at Atascadero State Hospital. During the time Allen taught, he was also disciplined for carrying a gun on campus.
[*] While working as a teacher, Allen used only one sick day. This was the day Cheri Jo Bates was stabbed to death at Riverside City College. This isn’t an official Zodiac killing but many people familiar with the case consider Bates the first murder of the Zodiac.
[*] Michael Mageau, who survived being shot in the face, neck and chest from a close range by the Zodiac, picked Arthur Leigh Allen out of a lineup. However, the lineup occurred 22 years after the attack. Allen also had access to the type of vehicle Mageau described the Zodiac arriving in.
[*] Allen’s shoe size was similar to footprints found in Zodiac crime scenes.
[*] Allen owned a Zodiac watch, which is where the symbol for the Zodiac is though to originate.
[*] Police officers thought that Allen’s gait was similar to that described by Zodiac survivors.
[*] Another Zodiac survivor, Bryan Hartnell, also said that Allen’s voice and stature (The Zodiac wore a hood during Hartnell’s attack) were a fit for the Zodiac.
[*] Allen had a 6 year friendship with a man named Don Cheney. Cheney said the friendship ended because he was creeped out that Allen might be the Zodiac killer. Cheney eventually went to the police and told them Allen had said he fantasized about killing couples at random, that he desired to be called ‘Zodiac’, that Allen signed his letters with the same symbol the Zodiac did, that he attached his flashlight to his gun in a similar manner to the Zodiac, and that he described preying on women by sabotaging their vehicle in a similar manner to Kathleen Johns and possibly Cherri Jo Bates.
[*] Allen had the same brand and model of typewriter that was used to write some of the Zodiac letters.
[*] Allen told the police that his “favorite” book was The Most Dangerous Game, a short story about a wealthy big game hunter who becomes bored of hunting animals and begins hunting humans instead. This book is referenced in one of the cyphers created by the Zodiac. Another one of Allen’s friends has said that Allen was “fascinated” by the idea of hunting humans.
[*] There is evidence that Arthur Leigh Allen may have been stalking Zodiac victim Darlene Ferrin. He told Don Cheney that he liked a waitress at the restaurant where she worked and she had told people about a man named “Lee”.
[*] On the day of the Lake Berryessa attack, Allen told police he was going to Lake Berryessa but changed his mind. He also said he had bloody knives, but that they were from butchering chickens.
[*] A search of Allen’s home found that he had drawn sketches of a bomb he could make. This type of bomb was referenced in Zodiac letters.
The evidence against Arthur Leigh Allen was considered circumstantial. Specifically, DNA and handwriting samples believed to belong to the Zodiac killer did not match Allen. He was never charged with the murders and passed away in 1992 from a heart attack. 
