Director Martin Scorsese's latest mob epic, "The Irishman," earned 10 nominations for the upcoming 92nd annual Academy Awards, but the attention has brought with it new scrutiny.

The movie is based on the 2004 book "I Heard You Paint Houses," which tells the story of self-described mob hitman Frank Sheeran.

Sheeran was a Philadelphia truck driver, who befriended Teamsters president Jimmy Hoffa. According to Sheeran, in July 1975 he fatally shot the infamous mobster.

Now, Sheeran's longtime lawyer and friend, Glenn Zeitz, told the Washington Post that Sheeran was not the killer.

“I’m clearly stating he did not shoot Jimmy Hoffa,” the 72-year-old semi-retired attorney told the Post. "Frank from the very beginning wanted to monetize his story."

In Fox Nation's docuseries "Riddle: The Search for James R. Hoffa," Fox News senior correspondent and anchor Eric Shawn investigated Sheeran's story and evidence that potentially contradicted it.

"Did Frank Sharon kill Jimmy Hoffa?" Shawn asked former Philadelphia mob boss, Ralph Natalie, in the Fox Nation show.

"No," Natalie laughed. "Not in a million years, no. ... He was a drunk and a Teamster. That's all he was. Every time you saw him he was drunk."

Shawn also sat down with the author of the book on which "The Irishman" is based, Charles Brandt.

"Who shot Jimmy Hoffa?" Shawn asked the former chief deputy attorney general of Delaware, who is also a former lawyer for Sheeran.

"Oh, Frank 'The Irishman' Sheeran, for sure," said Brandt.

"What would you say to someone who goes, 'Oh, he made it up? This is not true. He just wanted to sell a book,'" Shawn pressed.

"Just to understand basic principles of confession and corroboration," said Brandt. "And it's satisfied over and over again."

However, in the course of his reporting, Shawn came across a government document that raised serious questions.

"I discovered this Department of Justice memo that said someone else killed Hoffa," narrated Shawn in the Fox Nation show, "Salvatore 'Sally Bugs' Briguglio, a New Jersey mob hitman in the Genovese crime family."

ERIC SHAWN: MOBSTER'S SON SAYS HE KNOWS WHERE JIMMY HOFFA IS BURIED (AND WHO KILLED HIM)

That lead was corroborated by another man, who reached out to Shawn after watching his reporting on the Fox News Channel.

Phillip Moscato, Jr., son of Brother Moscato, who was a high-level associate in the Genovese crime family, told Shawn in "Riddle" that his father confessed to him that 'Sally Bugs' murdered Hoffa.

Moscato Jr. also claimed to know where Hoffa's body was buried.

To watch all of "Riddle: The Search for James R. Hoffa," go to Fox Nation and sign up today.

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