William Bulger was a “throwback,” reported 60 Minutes back in 1992, one of those colorful politicians who relished his job and seemed to know most of his constituents by name. Bulger had served in the lower house of Massachusetts’ legislature and as president of its Senate, and 60 Minutes showed him in all his anachronistic glory, crooning Irish ballads and marching in South Boston’s annual St. Patrick’s Day parade. Billy Bulger had grown up in “Southie” and never left, thriving in his public roles by mixing patronage and charm in the manner of his boyhood hero, the four-term Boston mayor John Michael Curly (inspiration for Edwin O’Connor’s famous 1956 novel, The Last Hurrah).

Bulger, however, did have one particularly “sensitive issue,” said the show’s longtime reporter, Morley Safer. It was his older brother Jimmy, a.k.a., Whitey, who happened to be “one of the most feared mobsters in Boston.” This Bulger was rarely glimpsed in public, said Safer, sticking mainly to the shadowy underworld where only criminals and cops were likely to go. You’d never see Whitey, the black sheep of the family, strutting with a shillelagh in a St. Patrick’s Day parade.

But in Black Mass, the new film directed by Scott Cooper, James “Whitey” Bulger hides in plain view. Vividly portrayed by Johnny Depp in something of a comeback role, Whitey spends much of his time at Triple O’s, a dingy South Boston bar, meeting with his mob pals Kevin Weeks (Jesse Plemons) and Stephen “The Rifleman” Flemmi (Rory Cochrane). By day Bulger and company drive deliberately along South Boston’s rough streets, stopping now and then to commit some public act of kindness, like helping an elderly neighbor carry her groceries. Whitey’s cruising also lets him keep tabs on his business interests, which revolve mainly around loan-sharking and gambling.

Nearly everyone in Southie knows that the hot-tempered Whitey Bulger has been in trouble with the law since high school. But many people—including his powerful brother—prefer to think of him not as a life-long hoodlum but a good-looking rogue who, it’s true, robbed a few banks back in the 1950s and did a stint in Alcatraz. But his heart, they decide, is in the right place. “He’s a good man,” declares Senator Billy Bulger (Benedict Cumberbatch) in Black Mass, adding “Jimmy’s business is Jimmy’s business, and it sure as hell is none of mine.”

Depp, for whom every movie is a costume party, plays Bulger with a prosthetic headpiece, piercing blue contact lenses, and a mouthful of rotten teeth. In several scenes he looks more like the vampire in the silent classic Nosferatu (1922) than the real-life Jimmy Bulger, who in photographs from the 1970s and 1980s looks like a successful politician himself, or perhaps an executive with a corner office in Prudential Tower. Bulger exercises, is a moderate drinker, and lives with his mother, joining her some evenings for a game of cards. He has no vices, apparently, other than extorting people and sometimes beating them up.

But it’s Bulger’s reputation as a brainy bad guy and a leading member of Boston’s Winter Hill Gang that, in 1975, prompts the FBI to offer him a deal. Agent John Connolly (Joel Edgerton), who grew up in Southie admiring both of the brothers, wants to use Whitey as a “top eschelon” informant in the bureau’s accelerating war on the Italian mafia. In exchange for insider information and advice, Connolly and his supervisor John Morris (David Harbour) agree not to bring Whitey in. No murders, please, they stipulate. But for more mundane offenses, like shaking down bookies, Connolly and Morris imply that they will look the other way. Bulger’s opinion of informants is that they’re “the scum of the scum.” But he likes the idea of ridding the city of rival thugs. So he agrees. “Let the feds do our dirty work,” he decides.

Black Mass dramatizes the grim results of this risky pact. Initially, at least, it yields results. With Bulger’s help, the FBI wiretaps a mafia hideout in Boston’s North End. Underboss Jerry Angiulo is captured on tape boasting of crimes that will soon land him in jail. Connolly becomes a star in the press, a modern-day Elliot Ness. Doubts grow, however, when Connolly’s boss (Kevin Bacon) notes that the information coming from Whitey Bulger isn’t plentiful, and what there is is self-serving. Most of it duplicates street gossip delivered by other, less prominent, rats. Bringing Bulger “into the tent,” in the agents’ hope-filled description, starts to look like a bad idea. Whitey, it appears, gains more than he gives.

The film is full of strong performances, and the Australian Edgerton stands out as agent John Connolly. His Boston Irish accent is perfect, and he precisely conveys the swagger of a man inflated by an unsteady mix of self-delusion and vanity. Connolly, who sports flashy suits and a pompadour, boasts of being “a kid from the streets.” He still idolizes Whitey Bulger, dining occasionally with the mobster and accepting his gifts. This infatuation puzzles Connolly’s wife Marianne (Juilanne Nicholson), since Bulger makes her skin crawl. “It’s Jimmy this and Jimmy that,” Marianne Connolly complains. She knows her husband and Morris are playing fast and loose with the bureau’s rules.

Under the FBI’s umbrella, Bulger expands his operations to include running guns to the Irish Republican Army and extorting protection money from cocaine dealers working the streets of South Boston. He uses his muscle to skim cash from a legal betting operation, World Jai Alai, which stages racquetball-like matches in Miami and elsewhere. Not least, he kills those who dare cheat or betray him, strangling some in basements and shooting others in broad daylight. Bulger and his henchman Flemmi dispose of their victims in marshy land near the Southeast Expressway. Then Whitey naps.

As Black Mass proceeds, Depp’s get-up comes to seem fitting for a man with such a relaxed approach to inflicting death. Beneath his everyman mask, Bulger is truly frightening, prompting extra panic among those he suspects of singing to the authorities. This becomes clear when one of his terrified colleagues, Brian Halloran (Peter Sarsgaard), pleads with an FBI agent for protection from Bulger’s gang. Unfortunately for Halloran, that agent is Connolly, whose lack of interest in Whitey’s activities turns inevitably to complicity in Whitey’s crimes. Halloran, too low on the criminal totem pole to arouse Connolly’s concern, ends up dead, gunned down in a car along with an innocent neighbor who made the mistake of offering him a ride.

Gangster movies like Scarface (1932) or Little Caesar (1931) endlessly repeat “fixed dramatic patterns,” the critic Robert Warshow wrote many years ago, including the main character’s “steady upward progress followed by a very precipitate fall.” Bulger’s life mirrors the genre’s conventions. After learning from Connolly that an arrest warrant was issued for him, Bulger would skip town with a longtime girlfriend, Catherine Greig, and spend the next 16 years on the lam, assuming a series of false identities. Bulger and Grieg managed to tour London and Louisiana, among other places, before landing comfortably near a beach in Santa Monica, California.

His fall did come abruptly, when he was cornered by U.S. Marshalls in his apartment building’s parking garage. Bulger was 81, unarmed, and surrendered without a fight.

Cooper’s film ends with the fugitive’s surrender in 2011. By then, he was very probably the most notorious American gangster since Al Capone. As soon as he vanished in 1994, Whitey Bulger’s story began to appear regularly in popular magazines and on television crime shows like America’s Most Wanted. Viewers were no doubt surprised to see that, by the time he was nabbed, Bulger appeared to be just another mild-mannered retiree—albeit one who stored a sawed-off shotgun in his spotless apartment, along with some hand grenades and over $800,000 in cash.

In 2006, Martin Scorsese’s The Departed was widely promoted as a dramatization of the Bulger story, with Jack Nicholson as the raging, lecherous Boston crime lord. But it really wasn’t, for its plot closely followed that of a Hong Kong crime drama, Infernal Affairs (2002), and Frank Costello, Nicholson’s character, owed more to the actor’s own overripe screen persona than to the real-life Whitey Bulger.

Black Mass stays closer to the real events than did the glitzy Scorcese film, and it’s one of the things that make the former a much more interesting film—in fact one of 2015’s best. Black Mass is based principally on Dick Lehr and Gerard O’Neill’s book of the same title. Lehr and O’Neill, reporters for the Boston Globe, began focusing on Bulger back in the late 1980s, when they took note of his remarkable ability to avoid arrest.

Not surprisingly, Boston rumors linked Whitey’s “luck” to the influence of his politician brother William—who, in ambiguous testimony before a 2003 congressional committee, continued to insist that concern for his brother’s welfare did not extend to helping conceal his felonies. The movie is ambiguous on this point as well. In fact, according to Lehr and O’Neill, the theory that Whitey’s real protectors were within the FBI was widely circulated, at least among state and local law-enforcement officials who often ran into roadblocks when investigating Bulger and Flemmi’s activities.

As good as it is, Black Mass the movie necessarily condenses a true crime story that is almost unbelievable in its strangeness and scope. Many an unlikely part of Whitey Bulger’s biography was not shoe-horned into the film—his extensive correspondence, for example, with the late Robert Drinan, a Jesuit priest who later became a U.S. Representative and a leading critic of the Vietnam War. Drinan and Whitey exchanged many letters back in the 1950s, when Bulger was in Alcatraz, reading Machiavelli and Kant and assuring family and friends outside that he had ambitious plans for going straight.

While in Alcatraz, Bulger had participated in the CIA-funded “MK Ultra” program, ingesting large amounts of LSD for what he was told was medical research. Whether or not the drug affected his long-term mental health, it is clear that Bulger became a Jeckyl and Hyde, living one part of his life as a mob boss and the other as a suburban householder liked by relatives and friends, upon whom he often bestowed expensive gifts. It’s not surprising that some family members, and others who never saw his monstrous side, assumed that Jim Bulger was a just a regular guy.

He always claimed that he was not an informant but had earned his leeway the old-fashioned way—with bribery. Certainly his relationship with FBI agent Connolly became unconscionably close. As Kevin Cullen writes in Whitey Bulger: America’s Most Wanted Gangster and the Manhunt that Brought Him to Justice (2013), Bulger gave Connolly over $200,000 and even vacationed with him in Mexico. In 2008, Connolly was convicted of second degree murder; the victim was an accountant who also made the mistake of doing business with Bulger’s syndicate. Unfortunately, as Cullen notes, many other FBI agents and supervisors who had also “winked and nodded” at Bulger’s activities, and even accepted his gifts, were never charged because “the statute of limitations had run out on all of them.”

In 2013, James “Whitey” Bulger was found guilty of 11 murders and other crimes related to his extensive racketeering. Since then, books about him have continued to appear. Journalists, social historians, and former criminals who broke the law with Whitey have all detailed his malign influence in a Boston that, after 25 years of unceasing gentrification, has all but disappeared. Bulger reportedly spends his days in a federal prison in Florida writing away—conducting an active correspondence with lawyers, old fellow Alcatraz inmates, and, apparently, schoolkids doing research on recent historical figures. And he’s thinking of writing his memoirs.

According to news reports, he recently answered an inquiry from some Massachusetts high schoolers seeking his thoughts on the role of leadership in criminal gangs. He told them to change topics and write about someone else. “My life,” his neatly handwritten letter declares, “was wasted and spent foolishly, and brought shame and suffering to my parents and siblings.” If Bulger does write his autobiography, he will surely find that summarizing such a long story, packed with so much murder, betrayal, corruption, and deceit, won’t be easy. But at least he’ll know how it ends.