The Zodiac Killer Theories in Based on a True Story, Explained

It’s one of the most famous unsolved murder cases in America: The Zodiac Killer.

The unknown suspect brutally murdered five people in California’s Bay Area in 1968 and 1969 and sent a series of cryptic notes to local newspapers, according to the FBI. The identity of the Zodiac Killer has eluded police and the public for years — but there’s no shortage of theories, several of which were discussed in Peacock’s new series, Based On A True Story.

While Kaley Cuoco’s character, Ava Bartlett, was at CrimeCon (a real event happening in September 2023, and presented by Oxygen), she met a fellow crime junkie and the two discussed Zodiac Killer suspects. The names Gary Francis Poste, Arthur Leigh Allen, and Richard Gaikowski come up. Who are these Zodiac Killer suspects in real life?

Zodiac Killer followers were abuzz in May 2023 when a volunteer group of cold case investigators called “Case Breakers” claimed a whistleblower told them Gary Poste was listed as a suspect by the FBI in the Zodiac killings, despite the FBI noting the case is still unsolved.

"The case remains open and there is no new information to report," an FBI spokesperson told NBC News.

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The group claims the Air Force veteran, who died in 2018, is the killer, based on a series of photographs dating back to 1963 that show forehead scars that the team thinks match marks made on a police sketch of the killer, according to their website. They also claim if you remove the letters of Gary Francis Poste’s name from one of the ciphers left by the Zodiac Killer, it reveals an alternate message.

Case Breakers also alleged they found DNA on a hiking mat once owned by Poste and connected it to him with DNA from one of his relatives, according to Newsweek. The group wants law enforcement to compare that DNA to hairs found on Cheri Jo Bates, who is believed by some to be a sixth victim of the Zodiac Killer. However, police previously said they don’t believe that case is related.

Schoolteacher Arthur Leigh Allen was the only suspect ever publicly identified by law enforcement in the Zodiac Killing case. He  died in 1992, according to SFGate.

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Allen was allegedly in the area of Lake Berryessa when Bryan Hartnell and Cecelia Shepard were attacked in September 1969, and was interviewed by Vallejo Police soon after but he said he was scuba diving at the time, according to the Daily Mail.

In 1971, his friend told police Allen had allegedly expressed desires to kill and used the name Zodiac, the news outlet reported, and his home was searched. In 1974, he was arrested for sexually assaulting a 12-year-old boy and served two years in prison.

In 2002, San Francisco police were able to get a partial DNA profile from the saliva on the stamps and envelopes the Zodiac killer sent to media. It was tested against Allen’s DNA and was not a match, according to SFGate.

Despite the lack of DNA evidence, Allen was featured as the serial killer suspect in the 2007 David Fincher movie, Zodiac.

One name sticks out to the founder and publisher of ZodiacKiller.com: Richard Gaikowski.

Tom Voigt created the website in the late 1990s to focus on the unsolved murders. He was later a consultant in the 2007 movie Zodiac, and his site was featured on America’s Most Wanted, according to an interview he did with Portland Monthly.

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His top Zodiac Killer suspect is Richard Gaikowski. Gaikowski moved to the Bay Area in 1963, and was a newspaper reporter and editor, according to Portland Monthly. In 1971, he was involuntarily committed to the Napa State Mental Hospital and diagnosed with a mental illness. He later operated a movie theater before dying in 2004.

When Gaikowski was a reporter for the Martinez Morning News Gazette, he was just minutes from two of the Zodiac crime scenes, Voigt argued to Portland Monthly. Zodiac victim Paul Stine’s sister also told Voigt she recognized Gaikowski attending her brother’s funeral.

The arguments don’t end there. A sister of victim Darlene Ferrin claimed one of her sister’s boyfriends was a journalist named Richard, according to Portland Monthly. And Mike Mageau, who survived the attack in which Ferrin was murdered, claimed the man who chased him then shot him was a friend of hers named Richard.

Voigt argued to Portland Monthly that the FBI looked into Gaikowski as a suspect, but dismissed him after he said he’d been in Europe during the first murder, despite Gaikowski losing his passport. He told the outlet he believes authorities need to take another look at Gaikowski as the serial killer.

In Based On A True Story, Cuoco and her fellow crime junkie decide s the most likely Zodiac Killer.

Richard Gaikowski i has never been named a suspect, and the Zodiac killings remain unsolved to this day.

Watch all episodes of Based On A True Story, streaming now on Peacock.