But the jury found the government had not proved its case against him in seven murders, and in one case it made no finding, leading to gasps inside the courtroom by relatives of those murder victims and explosive scenes outside the court.
"My father just got murdered again 40 years later in that courtroom," said the son of William O'Brien, whose name is also William.
When Mr. Bulger was led from the courtroom, he gave a thumbs-up sign to a few of his family members who were seated behind him, prompting a woman sitting with relatives of victims to yell out, "Rat a tat Whitey."
As a clerk read the verdicts in the lengthy and complicated list of charges, Mr. Bulger looked away from the jury and showed no reaction. His sentencing is set for Nov. 13.
The verdict delivered long-delayed justice to Mr. Bulger, who disappeared in 1995 after a corrupt agent with the Federal Bureau of Investigation told him he was about to be indicted. When he fled, he left behind a city that wondered if he would ever be caught — and even if the F.B.I., which had been complicit in many of his crimes, was really looking for him.
Mr. Bulger's lawyer, J.W. Carney Jr., said they would appeal the verdict because he had not been allowed to argue that he was given immunity for his crimes; his lawyer maintained that in essence, Mr. Bulger had a license to kill. Prosecutors scoffed at this notion of a defense, and the judge refused to allow him to raise it.
Perhaps the one glimmer of gratification for Mr. Bulger was that the jury reached "no finding" on the death of Debra Davis, one of two women he was accused of strangling to death. He has long maintained that his personal code of honor did not allow for the killing of women, although the jury did determine that he had killed the other woman, Deborah Hussey.
Mr. Bulger was found guilty on all but one of the 32 counts in his racketeering indictment; the one count on which he was found not guilty involved extortion. One of the counts alleged that he had committed 33 separate criminal acts, 19 of which were murders.
"The verdict reflects a jury methodically navigating through the charges," said Martin Weinberg, a prominent criminal defense lawyer in Boston. He said the jurors "rejected those that were based on uncorroborated accomplice testimony," mostly from decades ago.
But the jury also rejected the defense's argument that "because the F.B.I. was corrupt, Mr. Bulger deserved to be exonerated," Mr. Weinberg said.
Mr. Bulger was on the run for 16 years, until the authorities found him in 2011 in Santa Monica, Calif., with an arsenal of weapons and $822,000 in cash secreted in the walls of his apartment.
The trial was the final reckoning for a man small in stature but large in legend, who held the city in his thrall even in his absence, even after ruining hundreds of lives and deepening the stain on Boston's already corrupt federal law enforcement bureaucracy.
He had spent much of the trial scribbling on a yellow legal pad, perhaps for an appeal or a memoir, or maybe just for something to do. Some of the witnesses, particularly those who were testifying against him, had made him bristle with anger, and on a few occasions he exchanged obscenities with them, as if the courtroom were a schoolyard.
In his last few appearances in court, after deciding that he would not take the stand in his own defense, Mr. Bulger seemed defeated. He slumped more in his chair. He did not take notes as vigorously.
The guilty verdicts bring down the curtain on the city's most notorious gangster and a reign of terror enabled by the F.B.I.
"This was the worst case of corruption in the history of the F.B.I.," said Michael D. Kendall, a former federal prosecutor who investigated some aspects of Mr. Bulger's activities. "It was a multigenerational, systematic alliance with organized crime, where the F.B.I. was actively participating in the murders of government witnesses, or at least allowing them to occur."
Though previous courtroom proceedings — notably those presided over by Judge Mark L. Wolf in Federal District Court in 1998 — exposed the symbiotic relationship between Mr. Bulger's Winter Hill gang and the F.B.I., this trial focused more on Mr. Bulger's criminal actions while under the bureau's protection.
Over the course of the trial, Fred Wyshak, the assistant United States attorney, led the jurors through the 19 murders in which Mr. Bulger was accused of participating. The jury found the government had not proved its case in seven of the killings and had no finding in the other case.
The prosecution alleged that some victims were killed because the F.B.I. had told Mr. Bulger that they were informants who were going to testify against him. Others were rival hoodlums or innocent bystanders.
Some were lured into traps and shot. Others were felled in a hail of bullets. Some were bound in chains and shot at close range. Two women were strangled. Afterward, Mr. Bulger would routinely take a nap while others cleaned up the mess, which included removing the teeth of victims so their bodies could not be identified. The corpses were shoveled under the dirt floor of a basement or tossed into a car trunk and dumped in a shallow grave.
Beyond the murders, there were guns in people's faces and in their crotches. There were threats, shakedowns, demands for "rent" for the privilege of doing business on Mr. Bulger's turf.
"The depth of depravity is stunning — the killing of weak people, the women, the treachery against their own friends, shooting them in the back of the head," said Anthony Cardinale, a criminal defense lawyer who has represented mobsters and who first exposed Mr. Bulger as an F.B.I. informant. "It's almost Tosca-esque in terms of the treachery that went on and, in the end, everyone winds up dead."
The trial gave a glimpse into a time and place that had all but disappeared into the history books. The South Boston of Mr. Bulger's day would be almost unrecognizable now. It has been transformed from a parochial, working class enclave into part of Boston's booming innovation economy. Old triple-deckers have given way to glassy condos for a new wave of young professionals.
The dilapidated waterfront of Mr. Bulger's youth, where he once imported 36 tons of marijuana, is now a showcase harbor dotted with pleasure craft and rimmed by the soaring glass side of the federal courthouse where he has stood trial and where his former partners in crime have paraded in to testify against him.
"When you hear about those days, it's as if all that took place in another century, on another planet," said Thomas J. Whalen, an associate professor of social science at Boston University. "Those were the bad old days of Boston, and there is nothing to be nostalgic about. There was brutality at every level."
Also unrecognizable now is Mr. Bulger's self-created legend as the guardian of his neighborhood, a benevolent kingpin who used machine guns to keep out drug dealers and gunrunners. In fact, as his own lawyer told the jury, Mr. Bulger was steeped in the narcotics trade and made "millions upon millions" of dollars from it.
"This trial helped burst the bubble of idolizing those times and recognized the true hardships that he caused," said Michael Cassidy, a former state prosecutor and now a professor at Boston College Law School. "Many families were devastated by the drugs and crime, and it's important for the city not to have a false memory of what was going on. These weren't the glory days."
Mr. Cassidy said he hoped the verdict would ease some of the tensions that Mr. Bulger had provoked among local, state and federal law enforcement officials. "There was incredible animosity between the F.B.I. and the state police," he said. "The police were investigating the Winter Hill gang at the same time the F.B.I. was protecting them, and that has left so many festering wounds."
Those wounds are also visible among family members of the victims. Many have come to court every day and commented as a Greek chorus after each witness. While expressing disdain for the defendant, they have regarded the prosecution with skepticism and disappointment — they wanted the government to admit its own culpability.
Some legal experts, however, said the argument about government corruption was a diversion.
"This trial was not the forum to expose and condemn that F.B.I. conduct," said Rosanna Cavallaro, a professor at Suffolk University Law School. "In some ways, the government was able to frame it in a way to control and minimize the dark role the F.B.I. played. But the focus here is not what you are owed by the F.B.I., it's what you did that was criminal."
Still, Mr. Bulger's defense team based its closing arguments almost entirely on anger toward the government, even tossing in a reference to the Internal Revenue Service, though it had nothing to do with the case.
Mr. Carney and Hank Brennan, the defense lawyers, described a culture in which agents took bribes, alerted criminals in advance to wiretaps and pending indictments, and gave them information about informants that led to their murder. The lawyers urged the jury to stand up to what they said was governmental "abuse."
They produced little or no evidence that Mr. Bulger could not have committed the crimes of which he was accused. But Mr. Bulger seemed to view the trial as more about his legacy than his guilt or innocence. He wanted the world to know that he was not an informant, though that would have been no crime and was not part of the indictment against him.
