Greg King is the author of “The Last Voyage of the Andrea Doria: The Sinking of the World’s Most Glamorous Ship,” due out in April.

On a sweltering morning 50 years ago this month, a maid arriving at a secluded Beverly Hills estate found a scene of horror: five dead bodies strewn about the isolated house, among them pregnant actress Sharon Tate, who had rented the property with her husband, director Roman Polanski. Blood was everywhere; it had even been used to scrawl the word “pig” on the house’s front door. The next night, grocery store owner Leno LaBianca and his wife were slaughtered in similar fashion, the killers again leaving bloody messages, including a misspelled “Healter Skelter.” America was terrified.

Nearly four months passed before the killers were arrested, a strange group of flower children who had lived at an abandoned movie ranch under the spell of their leader, Charles Manson. The murders had been bizarre, but the alleged motive argued by prosecutor Vincent Bugliosi in court and expanded in his best-selling book, “Helter Skelter,” was even more so: an ex-convict who claimed to be both Jesus Christ and Satan, whose (mainly) middle-class followers had seemingly turned into drug-addicted zombies and killed to bring about the end of the world. The Bible and the Beatles’ song, Manson held, both predicted a race war, during which he and his so-called Family would live in a bottomless pit in the desert before emerging to rule the world. But as journalist Tom O’Neill shows in his new book, “Chaos,” Bugliosi’s flamboyant theory, rather than revealing the truth, merely concealed a tangled mass of contradictory motives in this most infamous of American crimes.

Conspiracy theories have ringed the Manson case since 1969, with allegations of drug deals gone bad, CIA-sponsored mind control experiments, celebrity sex tapes and revenge after producer Terry Melcher (Doris Day’s son, who had previously lived at the Tate house) did not give the cult leader a recording contract. It’s a confusing, often conflicting journey, as I learned writing my 2000 biography of Tate. O’Neill attempts to burrow deep beneath the surface of the murders. This isn’t so much a history of the crimes as it is a chronicle of his investigation. It started as a feature for now-defunct Premiere magazine in 1999; it took O’Neill 20 years of intensive research, and hundreds of interviews, to bring his story to its ambiguous conclusion. Along the way, he found legal misconduct, suppressed information and loose connections suggesting a much darker picture of what may have led to the 1969 murders.

It’s probably no accident that this book appeared after Bugliosi’s death in 2015: O’Neill uncovered troubling indications that the prosecutor may have withheld evidence from the defense and perhaps suborned perjury, strong-armed witnesses and lied during the trials, in an effort to strengthen his “Helter Skelter” motive. “Much of what we accept as fact,” O’Neill writes of the case, “is fiction.”

Some of O’Neill’s discoveries are stunning, especially when he’s discussing the inexplicable leniency shown by law enforcement officials and by Manson’s parole officer. Both before and after the August murders, Manson and several members of his group were arrested for various crimes but never charged. O’Neill speculates that this may have led to some sort of later coverup, meant to conceal the fact that inaction may have resulted in additional deaths.

There’s also a previously unknown telephone call that may have set the Tate-LaBianca murders into motion. In late July 1969, Manson associate Bobby Beausoleil and two female “Family” members killed musician Gary Hinman. Hoping to cast blame on the Black Panthers, they’d left the message “Political Piggy” scrawled on a wall in Hinman’s blood. On Aug. 8 Beausoleil made a jailhouse call to his fellow cultists: He’d been arrested for Hinman’s murder and needed “help,” adding, “Leave a sign.” Manson repeated this admonition to the foursome he sent to the Tate house just hours later; the “sign” took the form of “pig” written in Tate’s blood on the front door, presumably in the hope that police would think Hinman’s killer was still on the loose. O’Neill confirmed the call with two former detectives who, thinking (rightly) that they’d linked the Hinman and Tate murders, found their inquiries quashed by superiors. Other details, though, are less convincing, including claims, decades after the fact, that a shadowy figure (and possible CIA agent) knew of the Tate murders before the maid discovered the bodies.

O’Neill worries that his explorations make him “one of ‘those people’: an obsessive, a conspiracy theorist, a lunatic.” Indeed, the last third of the book tosses in shadowy figures and their possible connections to Manson. There’s the CIA, hoping to use unwitting hippies in San Francisco to study the effects of LSD; the director of the Haight-Ashbury Free Medical Clinic, investigating whether amphetamines led to violence; and even suggestions that a man tied to Lee Harvey Oswald assassin Jack Ruby may have crossed paths with Manson and used him in some kind of unofficial mind-control investigation. It’s all intriguing, perhaps even suggestive of some dark motive behind the murders, but O’Neill is unable to make the connections or even reach any firm conclusions: “I didn’t have a smoking gun,” the author admits.

There’s plenty of new information that makes “Chaos” a worthwhile addition to the canon of Manson literature, even if it ends without a unified theory of the crimes and their motivations. “My goal isn’t to say what did happen,” O’Neill explains, “it’s to prove that the official story didn’t.” In that he succeeds. Helter Skelter may no longer convince as a motive, but, with Manson’s death in 2017, it is unlikely that history will ever penetrate the remaining mysteries surrounding the grisly events that summer of 1969.


Charles Manson, the CIA, and the Secret History of the Sixties

By Tom O’Neill

Little, Brown. 520 pp. $30