BOSTON — Reputed gangster James "Whitey" Bulger was a "hands-on killer" responsible for "murder and mayhem" in Boston for almost 30 years, a federal prosecutor told a jury Wednesday as Bulger's highly anticipated racketeering trial began.

Bulger's lawyer acknowledged that Bulger made millions through drugs, illegal gambling and loan-sharking, but told the jury that three ex-mobsters who have pinned murders on Bulger cannot be believed. Each of the men received "extraordinary" deals from prosecutors in exchange for their cooperation, defense attorney J.W. Carney Jr. said.

The defense also denied prosecution claims that Bulger was an FBI informant for years and provided information on the rival New England Mafia.

Bulger, now 83, was one of the nation's most wanted fugitives when he fled Boston in 1994 after receiving a tip from his former FBI handler, John Connolly, that he was about to be indicted. He was finally captured in 2011 in Santa Monica, Calif., where he had been living with his longtime girlfriend in a rent-controlled apartment.

The defense went after the three once-loyal Bulger cohorts who are expected to be the prosecution's star witnesses: convicted hit man John Martorano, former Bulger partner Stephen "The Rifleman" Flemmi and former Bulger lieutenant Kevin Weeks.

Carney said Martorano, who served 12 years in prison after admitting to killing 20 people, was able to dictate the terms of his deal with prosecutors.

"The federal government was so desperate to have John Martorano testify ... they basically put their hands up in the air and said, 'Take anything you want,'" Carney said.

Kelly said Bulger headed the Winter Hill Gang, a violent group that "ran amok" in Boston for three decades, killing 19 people, extorting millions of dollars from drug dealers and other criminals, and corrupting police and FBI agents.

"At the center of all this murder and mayhem is one man — the defendant in this case, James Bulger," Kelly said.

Kelly offered chilling details of several of the killings, including the 1984 shooting death of John McIntyre. Authorities say he was killed after Bulger learned he had become an informant.

Kelly said Bulger chained McIntyre to a chair, interrogated him at gunpoint for hours, then tried to strangle him with a rope, but it didn't kill him.

"Bulger asks him, 'You want one in the head?' and McIntyre says, 'Yes, please,'" Kelly said.

Bulger then shot McIntyre, he said.

Kelly also described how Bulger allegedly strangled two 26-year-old women: Debra Davis, Flemmi's girlfriend, and Deborah Hussey, daughter of Flemmi's common-law wife.

Flemmi has testified previously that he watched Bulger kill both women. Weeks testified that he was also present when Bulger killed Hussey.

Bulger, Kelly said, was a "hands-on killer who was the leader of an extensive criminal enterprise."

Bulger's lawyer, however, said Flemmi is the one who killed the women and decided to pin the murders on Bulger after Bulger fled Boston in 1994.

Carney said Bulger had no motive to kill Davis or Hussey, who were close to Flemmi, but not Bulger.

Carney insisted that Bulger was not an FBI informant but instead paid FBI agents to tip him off when he and his gang were being investigated or about to be indicted.

"James Bulger never, ever — the evidence will show — was an informant," Carney said.

Carney said it went against Bulger's Irish heritage to be an informant. He also said Bulger was not close enough to members of the local Mafia to provide any useful information to authorities.

Carney said former FBI agent John Connolly — who was convicted of racketeering for tipping Bulger and Flemmi to an indictment — fabricated a lengthy FBI informant file for Bulger to cover up the fact that he was regularly seen meeting with Bulger.

Kelly said Bulger's gang succeeded by instilling fear in other criminals and corrupting Connolly and other law enforcement officials.

"It was part of a strategy they had, and it worked for them," Kelly said.

Kelly slowly read the names of each of the 19 victims while showing their pictures to the jury.

The first prosecution witness, retired state police Lt. Robert Long, identified surveillance video and photos of Bulger taken during a 1980 investigation. The video showed Bulger meeting with various organized crime figures at an auto repair garage in Boston's North End.

Testimony was set to resume Thursday.