The case ofthe Zodiac Killercaptured the imagination of the country in the late 1960s and early ’70s, but in no region more than in Northern California. The serial killer’s four attacks, which resulted in five deaths, took place here, and The San Francisco Chronicle covered the story extensively.

Reporter Paul Avery (played byRobert Downey Jr. in David Fincher’s 2007 film, “Zodiac”) even became part of the story, when the Zodiac started sending his letters and cryptograms directly to him.

Yet despite the focused attention of the public, the media and law enforcement, the Zodiac was never found, and thus the case has never really gone away. It continues to haunt the collective mind, like the Shakespeare authorship question and John F. Kennedy’s assassination.

但是现在有一个新的孔雀的纪录片,“神话of the Zodiac Killer,” that comes up with a novel explanation for why the Zodiac Killer was never caught: He never existed.

A crackpot theory? Maybe, but maybe not entirely.

The two-part docuseries takes, as its launching point, the self-published book, “The Myth of the Zodiac Killer: A Literary Investigation,” by Thomas Henry Horan, an English professor and former insurance investigator. Horan gets plenty of time to expound on his theory, but director Andrew Nock also brings in eyewitnesses, police investigators and a forensic psychologist to offer their opinions as well.

By the time the series is over, you’ll probably be where you started, not knowing what happened. But you may also suspect that Horan is on to something. He may push his ideas too far. He might have some details totally wrong. But his angle on the case is fresh — and may contain some truth.

Horan’s idea is basically that the “single killer theory” has been wrong from the beginning. He believes that the four violent incidents were committed by different assailants for different reasons. He points to the different ballistics, the different methods of killing and the widely varying descriptions of the killer by eyewitnesses.

As for the letters, Horan suggests that they might have been written by more than one person.

The multiple-killer theory makes some sense. Let’s say a murderer wanted to throw police off the scent of his own crime. What better way to do it than to send a letter in which the Zodiac claims responsibility for the crime? Now, instead of looking to solve a specific murder, the police will be looking for a serial killer.

Horan is pretty good at explaining why the same person might not have committed all the attacks. He’s on shakier ground when he tries to ascribe guilt. His notion that the murder of San Francisco cab driver Paul Stine, in Presidio Heights, might have just been a random robbery is at least plausible.

But he also says that drug-dealing bikers may have killed teenagers David Arthur Faraday and Betty Lou Jensen. He suggests that Darlene Ferrin may have been killed and Michael Mageau wounded by Ferrin’s ex-husband. He speculates that a masked park ranger may have fatally stabbed Cecelia Ann Shepard and wounded Bryan Hartnell.

Horan goes completely off the rails when he talks about the press. He hypothesizes that Avery might have written some of the Zodiac letters himself. Now, I was 10 years old when this story was unfolding, but years later I knew some of the bosses Avery worked under, and I can tell you that there is no way that could have happened. They wouldn’t have gone along with anything so dishonest, and such actions by a rogue reporter could never have slipped by them.

Horan further explains how pieces of Stine’s bloody shirt could have gotten into some letters sent to Avery: The reporter sneaked into the police evidence room and stole part of the shirt!

As for Horan’s evidence? Merely the fact that the Zodiac stopped writing to the San Francisco Examiner and other local newspapers and instead started writing exclusively to The Chronicle. (But really, why wouldn’t he choose The Chronicle over those other rags? The Zodiac may have been crazy, but he wasn’tthatcrazy.)

Still, “Myth of the Zodiac Killer” is an interesting documentary, and there just might be something to Horan’s theory.

Reach Mick LaSalle: mlasalle@sfchronicle.com