New book claims FBI knows Jimmy Hoffa's killer, but is keeping it secret Goldsmith said federal agents assigned to the case know who the real killer is.

A new book penned by Jack Goldsmith, a Harvard law professor and the former U.S. assistant attorney general, claims the FBI knows who killed legendary labor leader Jimmy Hoffa, but it won't admit that it blamed the wrong man.

In his new book, "In Hoffa’s Shadow," Goldsmith lays out his case for why he believes federal investigators allowed Chuckie O’Brien, the labor boss's protege, to be known as the key suspect in Hoffa’s mysterious disappearance in 1975, despite evidence proving otherwise.

Hoffa served as the president of the International Brotherhood of Teamsters labor union until 1971, making him a hero to many blue-collar Americans. He also had powerful enemies and ties to organized crime.

Goldsmith is also O'Brien's stepson.

The conventional wisdom was that O’Brien picked up Hoffa from the parking lot of the Machus Red Fox restaurant in Michigan on July 30, 1975, and drove him to his death, Goldsmith told Detroit ABC affiliate WXYZ in an interview Monday, a day before the book's release.

"There were good reasons for the FBI to suspect [O’Brien]. He had recently had a break with Hoffa, he was in the vicinity of the Machus Red Fox the morning of the disappearance, and the afternoon of the disappearance," Goldsmith told WXYZ.

"The last known time, when Hoffa was thought to be alive, did not leave enough time given the other things we know about Chuckie's whereabouts," he added, citing unnamed agents who worked on the case.

Goldsmith said federal agents assigned to the case know who the real killer is, but won't reveal the person's name due to embarrassment over accusing the wrong man.

"They just didn’t want to take the political heat, admitting they had basically accused the wrong person -- or let linger the accusations against Chuckie for 40 years," Goldsmith said.

The author did hint at who he has been told the real killer is, saying, "That person I learned was a low-level member of the Detroit family in the 1970s who rose to prominence and is no longer alive. Beyond that I’m not going to say anything else."

Periodic searches for Hoffa's body have always turned up empty, including one in a Detroit lumberyard in 2009; a Roseville, Michigan, driveway in 2012; and a farm in Oakland Township, Michigan, in 2013.

A new film about Hoffa's death and disappearance, "The Irishman," written and directed by Martin Scorsese and starring Al Pacino as the labor leader, premieres at the New York Film Festival this week and will be released on Netflix in November. Robert De Niro stars as Frank Sheeran, the titular character, who reflects on his role in Hoffa's murder. The real Sheeran died in 2003.