James “Whitey” Bulger, seen here in a police mug shot, insists he’s no rat in “Whitey: United States of America v. James J. Bulger.” (Magnolia Pictures)

As co-director of the “Paradise Lost” trilogy, Joe Berlinger raised so many questions about the seemingly rushed convictions of three Arkansas teens in a bizarre child-murder case that the prisoners were ultimately set free. Berlinger isn’t out to do the same with his latest documentary, “Whitey: United States of America v. James J. Bulger.”

“I’m not an advocate for James ‘Whitey’ Bulger,” Berlinger makes clear. “He’s a brutal, vicious killer who deserves to be behind bars.”

The notorious gangster spent 16 years on the FBI’s Ten Most Wanted list before his capture (at age 81) in 2011, and no one in the film denies that Bulger is a bad guy. Other truths proved more elusive, however.

“Of all the films I’ve ever made, this is a ‘Rashomon’ experience,” Berlinger says, referring to the 1950 Akira Kurosawa film that tells the story of a crime from multiple points of view, many of which contradict one another. “I think [‘Whitey’] is allowing everyone to have their say in the interest of a larger truth rising to the top, and that truth is there are a lot of disturbing questions about this case that deserve to be answered.”

With this film (available on iTunes and VOD), Berlinger questions how Bulger managed to rule Boston’s criminal underground as one of the chiefs of the Irish mob for decades when the police and the FBI knew full well what he was up to.

“If you believe the official story, he was an FBI informant and the FBI looked the other way and empowered one set of criminals to take down the other set,” Berlinger says (the “other set” was the Mafia). “Whitey” pokes really big holes in that official story — often with the help of Bulger himself, who repeatedly insists in talks with his lawyer (Berlinger was not allowed to interview Bulger himself) that he was not “a rat.” 

The catch is that Bulger and the government have such a huge stake in their stories being true that you can’t trust either of them. Bulger wants to keep his status as an honorable gangster who doesn’t tattle; the government wants to use Bulger’s status as an informant as justification for why they never caught him.

“[Bulger’s] trial really should have been an opportunity for all of the truth to come out as to how it is he could have been on top of the criminal heap for 25 years and not get so much as a traffic ticket,” Berlinger says. Bulger was not allowed to present his argument — basically, that while he wasn’t an informant, he had unofficial assurances from multiple branches of law enforcement that he wouldn’t be touched — as his defense.

Berlinger, most famous for exposing injustices perpetrated against the wrongly convicted, says the victim of injustice here isn’t Bulger, who is serving two life terms in federal prison. To him, the victims are the families of those Bulger killed, as well as the American public as a whole. 

“We can’t have our institutions of government picking and choosing who should live and who should die by deciding, ‘OK, we’re going to bring down the Italian Mafia, but we’re going to let the Irish mobsters run free,’ ” he says. “That’s why it matters.”