In 1968 and 1969, as San Francisco was bathing in the hot afterglow of the "Summer of Love," a serial killer was coldly stalking the Bay Area. The so-called Zodiac Killer — immortalized in the 2007 David Fincher film Zodiac — fatally stabbed or shot at least five people, then sent cryptic, taunting notes to the police and local newspapers until 1974. He was never caught, and the San Francisco Police Department officially closed the case in 2004. But now, retired California Highway Patrol officer Lyndon Lafferty has unofficially reopened it in a new book laying out the results of his and six colleagues' decades of freelance sleuthing. The book, The Zodiac Killer Cover-Up, purports to solve the case, claiming that the Zodiac Killer is still alive and living in the area. Here, six takeaways from Lafferty's investigation:

1. Lafferty won't name the suspect
The killer, Lafferty says, is a 91-year-old recovered alcoholic living in fairly comfortable retirement in nearby Solano County, where the killings began in December 1968. Lafferty says a lot about his suspect, but leaves out a crucial detail: His name. Citing privacy and safety concerns, Lafferty refers to the man by a pseudonym, George Russell Tucker. For any code-breakers interested in the truth, Lafferty says the killer spells out his real name in one of his signature zodiac-riddled letters to the cops and the press. 

2. Lafferty says he's known the man's identity since 1970
Lafferty stumbled into the case at a Vallejo rest area in 1970, he says, when Tucker parked next to his patrol car. The guy in the car looked like the sketches of the Zodiac Killer, Lafferty said, but there was something else: "I looked into a quivering, snarling face like I was looking to the face of death.... It scared the hell out of me." He ran the man's license number, and has been investigating him on and off ever since. Lafferty says he has provided the real name to the police, and waited to publish the book until some people had died, including Tucker's wife.

3. The evidence is plentiful, but circumstantial
Lafferty and his six colleagues — including a retired local cop who worked on the case and an ex–Navy intelligence officer — have spent more than 30 years on the case, and one chapter of the book lays out "156 circumstantial factors of evidence that related to the Zodiac case and our suspect," Lafferty tells ABC News. For example, Tucker frequented a restaurant where one of the victims, Darlen Ferrin, worked, and a witness recalls seeing a car similar to Tucker's lurking outside Ferrin's house in the weeks before her death.

4. Tucker's apparent motive? Revenge
Lafferty says the reason Tucker started killing people — the Zodiac Killer claimed to have murdered 37, far more than the official tally of five — is that he found his wife cheating on him with, among other men, a senior Solano County Superior Court judge. "Through his tauntings of the police, his code, ciphers, and letters, he was on a mission to redeem his shattered ego," Lafferty says in the book. "To prove that he is better, smarter, and more clever than all the judges and police put together."

5. Lafferty accuses local officials of a cover-up
As the name of his book suggests, Lafferty says "power brokers" in Solano — notably the senior judge sleeping with Tucker's wife — stymied the investigation. Cops were instructed not to "investigate this man until you have permission from the judge," Lafferty tells ABC News. James Dean, a retired Vallejo police detective who worked with Lafferty, says local cops actually started investigating Tucker... until they were suddenly waved off, with the explicit instruction: "Tear up your shit." This corruption and meddling, Lafferty concludes, gave "the insane Zodiac Killer immunity and a license to kill."

6. Of course, not everyone is convinced
"It seems that each year or so we get another claim about the true identify and/or whereabouts of the Zodiac Killer," says Brock Keeling at SFist. There's no reason this should be any more true than the others.

Sources: ABC News, Daily Republic, Independent, San Francisco Chronicle (2), SFist, Telegraph, TIME