Was Marilyn Monroe Murdered? Frank Sinatra Thought So.

In the nearly 60 years since Marilyn Monroe’s untimely passing, there’s been plenty of speculation over whether or not her death — the result of a barbiturate overdose that was ruled a “probable suicide” — was actually a homicide. As a new book reveals, one of her famous friends was among those who believed the iconic actress was actually murdered.

People magazine has a new excerpt from Sinatra and Me: In The Wee Small Hours, a memoir by Frank Sinatra’s former manager Tony Oppedisano. In it, Oppedisano claims that Sinatra was certain there was foul play involved in Monroe’s death. “Frank believed she was murdered,” he writes, “and he never got over it.”

The book says that Sinatra and Monroe were close friends but never romantically involved, noting that the crooner was often a confidante of the actress about her affairs with John F. Kennedy and Robert Kennedy. According to Oppedisano, “Marilyn told Frank she didn’t understand why they’d shut her out completely once she stopped having sex with them.”

The author notes that the weekend before her death, Monroe had rekindled her romance with Joe DiMaggio and was preparing a press conference to announce they were getting back together. But there were rumors that she was getting ready to spill details about her relationships with the Kennedys.

“Frank said she’d never have spilled about the Kennedys because she still had feelings for [Jack],” Oppedisano writes. “Frank believed if the press conference hadn’t been announced, she would have lived a lot longer.” The book asserts that Sinatra had multiple sources who told him “she’d been murdered with a Nembutal suppository and Robert Kennedy or the mob was involved.”

We’ll likely never know for sure what the truth is, but it’s clear that Monroe’s tragic death had a profound effect on Sinatra.