A documentary by Joe Berlinger. Rating unavailable.

The latest true-crime exposé from Joe Berlinger—who previously codirected such dark classics as Brother’s Keeper and the Paradise Lost trilogy—doesn’t spend much time on the psychology of its subject, but it doesn’t really need to. The movie is less a profile of the most vicious gangster in Boston’s underworld than it is about the institutions that nurtured, enabled, and protected him during a 30-year reign of terror that law-enforcement officials were in no hurry to end.

Born just before the big crash of 1929, the brutal, charismatic James “Whitey” Bulger worked his way up through Beantown’s notorious Winter Hill Gang. This was after stints in juvenile hall, army stockades, and Alcatraz. The movie doesn’t mention it, but Bulger claims he was also forced into a CIA experiment with LSD. If so, his mind didn’t expand much past murder, mayhem, and vast extortion rackets. He was sharp enough to take advantage of the early-’60s crackdown on the Italian Mafia—something FBI chief J. Edgar Hoover once claimed did not exist.

The local fed office shielded the increasingly cocky killer on the pretext that he was a reliable government informant. Through Bulger’s lawyers, crime journalists, and independent investigators, the movie debunks the notion that Bulger ever did more than cheer on the takedown of his mob rivals. In reality, the police were on his payroll. “Christmas is for kids and cops,” he’s quoted as telling one of his top lieutenants, who eventually turned on Whitey in court.

As the tale winds toward its subject’s 2013 trial—for 32 counts of racketeering, murder, and more—the pileup of witnesses, lawyers, and agents, plus victims and their families, gets slightly wearying. But the realization that so much corruption could go so deep for so long slaps you back to life.