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Prosecutors described reputed Boston gang boss James "Whitey" Bulger as "one of the most vicious, violent and calculating criminals ever to walk the streets of Boston" in the closing arguments of the longtime fugitive's racketeering trial, but his own lawyers sought to put the government on trial.

Bulger, 83, who spent nearly two decades on the run before an episode of "America's Most Wanted" led to his capture, is accused of leading the murderous Winter Hill Gang in the 1970s and '80s before dropping out of sight in 1994 ahead of a 32-count indictment. During nearly eight weeks of testimony in U.S. District Court, jurors have heard chilling testimony about 19 killings in which Bulger was allegedly involved as well as several other crimes.

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Early Monday, Bulger, who was captured with his longtime girlfriend living in Santa Monica, Calif., wore a long-sleeve, gray sweater and spectacles, scribbling notes as he sat next to his attorneys. Assistant U.S. Attorney Fred Wyshak, who hunted the one-time FBI informant for years, was expected to take nearly three hours to sum up their case, followed by Bulger's team's summation and finally, a 30-minute rebuttal from prosecutors. Wyshak focused on debunking the idea that Bulger was some sort of modern -day Robin Hood.

“This is not about a Robin Hood story about a man who keeps angel dust and heroin out of South Boston,” Wyshak said.

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    The prosecutor noted that evidence against Bulger came from his former cronies, including admitted hitman John Martorano and Bulger’s former partner, Stephen “The Rifleman” Flemmi. Both men implicated Bulger in multiple murders, some of which took place even after Bulger began secretly working with the FBI.

    “It does not matter that Mr. Bulger was an FBI informant when he put the gun to Arthur Barrett’s head and pulled the trigger,’’ Wyshak said. “Whether he was an informant or not, he’s guilty of murder.”

    Barrett was murdered in July 1983, allegedly for loot he'd taken during a 1980 bank heist.

    Wyshak, who used charts to demonstrate the Winter Hill Gang hierarchy, said the gang grew out of a street war that left Boston's streets bloody.

    "The reason this racketeering organization was so successful [was because] these men were survivors of a gang war in the 1960's during which 60 people died," he said. "These men were the victors. They were feared. They were armed to the teeth. They were like a paramilitary organization. They had stolen vehicles and back-up cars to crash into police.  They used walkie talkies. They hunted their prey. They hunted people.  They were the scariest people walking the streets of Boston."

    But Bulger attorney Hank Brennan said the government was using violent criminals like Flemmi and Martorano to build a shaky case against his client, criminals he said the FBI got in bed with decades ago.

    "If these men who testified are so bad why are they all walking around - walking our streets?" Brennan asked. "Is our federal government protecting us? What have they done? There has to be more to this story. Victim after victim who suffered at the hands of these men.

    "The prosecution stands before you and almost brags about tearing down this criminal structure," he continued. "So why did they let almost all of them go?"

    The defense also focused on attempting to rebut allegations that Bulger strangled two young women.

    The jury is expected to begin deliberations Tuesday after receiving instructions on the law from the judge.

    Bulger's girlfriend, Catherine Greig, pleaded guilty last year to charges related to helping him stay on the run for more than a decade and was sentenced to eight years in prison. She tried to have her sentenced reduced, saying people who claim their relatives were killed by Bulger shouldn't have been allowed to speak at her sentencing, but an appeals court panel found no basis to change the sentence.

    Fox News' Andrew Fone and Molly Line contributed to this report.