Documentarian Joe Berlinger sets out to investigate the great mystery in the saga of James J. "Whitey" Bulger, the fearsome Boston gangster who freely intimidated and murdered people for decades and then took 16 years as a fugitive from justice to be apprehended in 2011.

That question: Why'd it take so long to bust him?

The FBI maintains that Bulger was an informant, left alone to continue serving as a useful source of information.

The criminal himself, his defense team at his 2013 trial and the families of at least several victims insist otherwise, arguing that he was left alone because he had bureau agents in his pocket.

The documentary "Whitey: United States of America v. James J. Bulger" offers an avalanche of conflicting and complicated testimony, old photos, surveillance footage and pans across crime maps to unpack the labyrinthine maze of what actually happened during Bulger's underworld reign.

The movie doesn't get any closer to legitimate answers, if in no small part because there are none to be had. The evidence, as presented here, could be interpreted to support both theories. It's clear that the full story hasn't been told, that there's probably more to the FBI's involvement with this vicious murderer than the public record says.

The movie offers a sustained inquiry into a murky minefield. It offers a lot of facts, dates and opinions. But the flurry of information, which ultimately functions as white noise, doesn't exactly make for a satisfying moviegoing experience.