Former FBI agent John Connolly was convicted Thursday of second-degree murder for leaking information to Boston mobsters that led to the 1982 shooting death of a gambling executive who also had ties to gangsters.

Jurors deliberated less than three days before delivering the verdict following a two-month trial. The jury acquitted Connolly of conspiracy, but he still faces life in prison when sentenced Dec. 4.

Prosecutors said former World Jai-Alai president John Callahan was killed after Connolly warned gangsters that Callahan might implicate them in other slayings. Boston mob kingpins James "Whitey" Bulger and Stephen "The Rifleman" Flemmi were FBI informants handled by Connolly.

Connolly, who showed no emotion when the verdict was read, long denied involvement in Callahan's killing. Connolly was convicted in 2002 of racketeering because of his relationship with Bulger and Flemmi, including a 1995 tip that enabled Bulger to escape arrest and begin a life on the run that continues to this day. Bulger is one of the FBI's "Ten Most Wanted" fugitives.

The story that unfolded over the past two months in a Miami courtroom spanned more than two decades of Boston's underworld, a tale that has already spawned several books and was the basis for the 2006 Martin Scorsese film "The Departed." Matt Damon played a crooked Connolly-like law enforcement officer and Jack Nicholson was the Bulger-esque Irish-American mobster.

Connolly retired from the FBI in 1990 and was later indicted on federal racketeering and other charges stemming from his long relationship with Bulger and Flemmi, who paid the agent $235,000 over the years for protection, according to trial testimony.

In a case considered one of the FBI's worst failures, Connolly was convicted in 2002 and is serving a 10-year federal prison sentence in the corruption case. He was indicted in 2005 in the killing of Callahan, 45, whose body was found stuffed in the trunk of his Cadillac at Miami International Airport in August 1982. He had been shot at least twice.

Confessed mob hit man John Martorano testified that he shot Callahan — at one time a good friend — based on Connolly's warning that the gangsters would probably all go to prison if Callahan talked to the FBI about an Oklahoma businessman's killing a year earlier.

Defense lawyer Manuel Casabielle insisted that Connolly was innocent, that his job as a top FBI organized crime-buster meant dealing with unsavory characters — "top-echelon informants" in FBI parlance — who possessed sensitive information about top Mafia kingpins in Boston.

"Him and other agents like him were the tip of the spear in the fight against the Mafia," Casabielle told jurors in closing arguments.

But Flemmi, Martorano and other mob figures testified that Connolly made sure the gang was shielded from prosecution for numerous crimes, even multiple murders, and supplied information about possible turncoats or "rats" in their own ranks that needed elimination. Prosecutors said at least two other men who were FBI informants died violently because of Connolly's leaks.

"John Connolly swore an oath to the FBI and the United States of America," said prosecutor Michael Von Zamft. "He gave up that public trust because he decided he would rather be a gangster than an FBI agent."

Callahan was killed, according to testimony, because Connolly told them the FBI was about to apply pressure on Callahan to give up information about the 1981 killing of World Jai-Alai owner Roger Wheeler in the parking lot of a country club in Tulsa, Okla.

The gangsters feared Callahan would not hold up and might confess to the FBI that they were responsible for Wheeler's slaying. Callahan had wanted Wheeler dead so he could retake control of World Jai-Alai.

World Jai-Alai ran frontons in Florida and in Hartford, Conn

Flemmi is serving a life prison sentence and admitted to 10 murders. Martorano cut a deal with prosecutors by agreeing to testify against Connolly, and spent 12 years in prison after admitting to 20 murders, including the killings of Wheeler and Callahan. Martorano is now a free man.