Sex, psychedelica, and government experiments gone wrong… Why the real story of Charles Manson is so much crazier than anything in Once Upon a Time in Hollywood. Tom O'Neill, author of a major new Manson book, reports

I spent 20 years reporting on Charles Manson and his followers, who shocked the world fifty years ago when they murdered seven people in Los Angeles, including the actress Sharon Tate. The Manson Family followed their leader’s every command. In less than a year, Manson turned a group of peaceful hippies, mainly young women, into savage, unrepentant killers.

Their grisly crimes lit a flame of paranoia across America and have now inspired Quentin Tarantino’s latest movie, Once Upon a Time in Hollywood. But little is known about how Manson became Manson.

How had a barely literate ex-con, who had spent more than half his life in federal institutions, acquired the knowledge and resources to brainwash people? Even his prosecutor, Vincent Bugliosi, conceded that there had to be “some intangible quality or power that no one else has yet been able to isolate and identify.”

The answer could be in Manson’s crucial lost year in the Haight-Ashbury district of San Francisco, California – a year largely overlooked in the endless dissection of Manson’s crimes – where, during 1967’s summer of love, he began to drop acid and form his cult.