BOSTON — A prosecutor called reputed crime boss James “Whitey” Bulger “one of the most vicious, violent and calculating criminals ever to walk the streets of Boston” as he urged a jury Monday to convict Bulger of charges that include 19 killings during the 1970s and ’80s

Bulger’s lawyer countered by attacking the prosecution’s key witnesses — ruthless underworld figures who once were loyal Bulger associates but testified against him in exchange for reduced sentences.

Federal prosecutor Fred Wyshak, who pursued a case against Bulger for more than two decades, recounted grisly details of the killings Bulger is accused of committing or orchestrating.

Among the victims, he told the jury, were two men who were chained to chairs for hours, interrogated, then shot in the head, two women who were strangled, and two men who died in a hail of gunfire as they left a South Boston restaurant.

Wyshak said Bulger, as the boss of the Winter Hill Gang, South Boston’s Irish mob, was a hands-on killer who carried out many of the slayings himself.

He described the gang’s array of guns, knives, a souped-up “hit car” and walkie-talkies used when the group decided to kill someone.

“They hunted their targets,” Wyshak said in a closing argument that lasted more than three hours. “These men didn’t hunt animals, ladies and gentlemen, they hunted people.”

The jury is expected to begin deliberations on Tuesday after a nearly eight-week racketeering trial in federal court. In addition to the killings, Bulger, 83, is accused of numerous instances of extortion, money laundering and hoarding of guns.

Prosecutors say Bulger was secretly working as an FBI informant during the same period — a claim his lawyers have strongly disputed.

He fled Boston in 1994 after being tipped off by a retired FBI agent about his indictment and was one of the FBI’s most-wanted fugitives until he was captured with his longtime girlfriend in Santa Monica, Calif., in 2011.

His disappearance proved a major embarrassment for the FBI and exposed the bureau’s cozy relationship with its underworld informants. Investigators have said Bulger corrupted FBI agents and state police with payoffs while continuing to conduct his murderous business.

During closing arguments, defense attorney Hank Brennan attacked the prosecution’s chief witnesses: former hit man John Martorano, one-time Bulger protege Kevin Weeks and ruthless killer Stephen “The Rifleman” Flemmi.

Martorano and Weeks have completed their prison sentences and are now free. Flemmi struck a deal to avoid the death penalty and is serving a life sentence.

“You have to sit there and ask yourself — why are they still walking the streets? If they’re so vicious and violent and our government knows about it, why are they out there right now?” Brennan asked the jury.

During the trial, Bulger’s lawyers spent much of their time disputing allegations he was a “rat” who informed on the rival Italian mob and people in his own gang.

The defense also tried to counter allegations Bulger strangled two women — something he also apparently considered a violation of his underworld code of honor.

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