Lillo Brancato Jr, 32, appeared in six episodes of the mafia television series before his character, Matt Bevilaqua, was killed off. However, prosecutors argue that his mafia links continued when he befriended Steven Armento, a reputed member of the Genovese crime family who had been thrown out of the organisation over his drug addiction.
Brancato had enjoyed a promising film career after being "spotted", aged 15, on a New York beach by the casting director for A Bronx Tale, in which the young actor appeared with Robert de Niro. But his life reportedly took a nosedive as he was involved in two drug-related arrests and, finally, with the killing in 2005 of Daniel Enchautegui, a New York police officer.
Prosecutors allege that Brancato drove himself and Armento to the home of Mr Enchautegui's next-door neighbour, where they began stealing prescription drugs.
When confronted by the policeman, Armento shot him. Both Armento and Brancato were wounded.
Armento, 48, was convicted of first-degree murder and sentenced last week to life in prison without parole.
However, Brancato's lawyers claim his case is different. "Lillo didn't have a gun. Nor did he know anyone had a gun. Lillo wasn't burglarising anyone's home," said Joseph Tacopina, his lawyer. "It's a tragic case, it's tragic in a lot of ways. But that doesn't mean he's behind the crime."
Brancato denies second-degree murder and other charges in the trial, for which jury selection has begun.
Family and friends have said he is a good man with a drug problem, who was in the wrong place at the wrong time.
"He obviously had problems he kept well hidden, but that doesn't mean he should be held accountable for the actions of the man he was with, especially if that man was under the influence," said Chris Tardio, who also appeared in The Sopranos.
Thanks to Tom Leonard
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