The murder trial of a former FBI agent whose exploits helped inspire the Oscar-winning film "The Departed" began Monday with prosecutors saying that he was a corrupt friend of gangsters who passed along critical information that led to the slaying of a gambling executive.

While a hit man for Boston's notorious Irish mafia pulled the trigger that killed the gambling boss, John Connolly was equally responsible, prosecutor Fred Wyshak told a jury.

"He gave sensitive information to gangsters, who used that information to protect themselves. And (they) used that information to kill people. One of those people was John Callahan," Wyshak said of Connolly.

John Callahan was a 45-year-old former president of Miami-based World Jai-Alai,a Miami fronton, or facility, for the sport in which gamblers bet on players who sling a small ball against a wall using wicker baskets. His body was found Aug. 2, 1982, in the trunk of his silver Cadillac, parked at Miami International Airport.

Admitted hit man John Martorano has pleaded guilty to shooting Callahan and will testify about Connolly's role in the killing, Wyshak said.

Connolly, 68, faces life in prison if convicted of first-degree murder and murder conspiracy charges. Defense attorney Manuel Casabielle said the links are flimsy between Connolly and Callahan, a man he called "a brilliant accountant by day, a gangster wannabe by night." Bulger and his cohorts knew Callahan might talk, Casabielle said, and they made it a practice not to discuss killings with Connolly.

"They never, ever spoke of murder to any law enforcement officer in general, or Mr. Connolly in particular," he said.

Callahan was murdered, Wyshak added, because notorious Winter Hill Gang leader James "Whitey" Bulger feared he would tell authorities they were behind the 1981 killing of a businessman in a dispute over the jai-alai business. Martorano has also confessed to that killing.

Connolly is already serving a 10-year sentence for a 2002 federal racketeering conviction stemming from his long association with Bulger and other mobsters. Both men were FBI informants about rival Italian Mafia gangs in Boston with Connolly as their handler — and Connolly was convicted of protecting them in turn.

Bulger is charged in 19 murders. Now 79, Bulger is a fugitive on the FBI's "Ten Most Wanted" list; he fled in 1995 after being tipped off by Connolly, about an impending federal racketeering indictment.

Connolly associated frequently with Winter Hill Gang members, taking vacations with its leaders and accepting about $250,000 over the years from them, Wyshak said.

"The defendant, John Connolly, he's just another member of the gang. He's no different," the prosecutor said. "If they made a big score, the defendant got a cut."

Casabielle urged jurors to remember they won't hear testimony from Bulger.

"You will not be able to hear Mr. Bulger confirm that those statements were made," he said.

Numerous FBI agents who knew and worked with Connolly are expected to testify, along with Martorano and other Boston gangsters.

Martorano has confessed in court to 20 murders and served 14 years in prison after agreeing to cooperate in the Connolly case.

Bulger apparently planned for life on the run by leaving cash in safe deposit boxes around the world, including Florida, Ireland, England and Canada, authorities said. The last confirmed sighting of him, according to the FBI, was in London in September 2002.

Casabielle accused prosecutors of trying to use the long, sordid history of the FBI and Boston mobsters to convict Connolly of murder without enough evidence.

"It is not fair to take a bunch of mud and throw against an individual and hope some of it sticks," he said. "That is not justice."