MIAMI, Florida (CNN) -- Former FBI agent John Connolly, whose fall from celebrated mob-buster to paid gangland flunky captivated a South Florida courtroom for weeks, broke his long silence Thursday at his sentencing hearing.

Retired FBI agent John Connolly was convicted last month of second degree murder for his role in a mob hit.

Connolly, 68, denied having any role in a 1982 mob hit, telling the family of slain businessman John Callahan: "It's heart breaking to hear what happened to your father, and to your husband ... My heart is broken when I hear what you say."

Later, under a spirited cross-examination, Connolly explained that rubbing elbows with killers and gangsters and winning their confidence was part of the job. His attorney argued, "He did what the FBI wanted him to do and now all of a sudden, he's responsible for all these heinous acts."

Connolly did not testify at his trial. The prosecutor, Michael Van Zamft, asked for a life sentence, saying the 30-year minimum sentence is too little because "Mr. Connolly abused his badge."

Judge Stanford Blake postponed the sentencing until January 15. He said he needed time to consider a defense motion challenging the second-degree murder conviction.

Connolly was convicted last month in the 1982 slaying of Callahan, an executive with World Jai-Alai. Callahan's bullet-pocked body was found in the trunk of a Cadillac parked at Miami International Airport.

Connolly's testimony followed that of several other witnesses, including Callahan's son and a former FBI agent.

Callahan's son, Patrick, read letters that he, his sister, and his mother wrote. He said that his mother considered his father "the love of my life" for 23 years.

Former FBI agent Billy Reagan told the judge: "John had nothing to do with these murders, your honor."

During the two-month trial, jurors heard that Connolly had told his mob connections that Callahan, 45, was a potential witness against them, setting him up for the gangland-style execution.

Connolly previewed his denials in a jailhouse interview published Thursday in The Boston Globe. He faces 30 years to life at his sentencing.

"I did not commit these crimes I was charged with," Connolly told the newspaper. "I never sold my badge. I never took anybody's money. I never caused anybody to be hurt, at least not knowingly, and I never would."

According to testimony at his trial, Connolly was co-opted by the very gangsters he was supposed to be pursuing -- members of South Boston's notorious Winter Hill gang. His story is said to be the inspiration for the character played by Matt Damon in the 2006 Martin Scorsese movie, "The Departed."

Connolly's sordid tale has been closely followed in New England, where he grew up in Boston's "Southie" neighborhood, the same area long dominated by the Winter Hill gang and its notorious leader, James" Whitey" Bulger. Sought in 19 slayings, Bulger is the FBI's second most-wanted fugitive.

During the first two decades of his FBI career, Connolly won kudos in the bureau's Boston office, cultivating informants against New England mobsters. Prosecutors said Connolly was corrupted by his two highest-ranking snitches: Bulger and Stephen ''The Rifleman'' Flemmi.

Connolly retired from the FBI in 1990 and later was indicted on federal racketeering and other charges stemming from his long relationship with Bulger and Flemmi. He was convicted of racketeering in 2002 and was serving a 10-year federal prison sentence when he was indicted in 2005 in the Callahan slaying.

During testimony, jurors heard that Connolly was on the mob payroll, collecting $235,000 from Bulger and Flemmi while shielding his mob pals from prosecution and leaking the identities of informants.

The prosecution's star witnesses at the Miami trial were Flemmi, who is now in prison, and mob hit man John Martorano, who has admitted to 20 murders, served 12 years in prison and is now free.

Callahan, who often socialized with gangsters, had asked the gang to execute Oklahoma businessman Roger Wheeler over a business dispute, according to testimony. Martorano killed Wheeler in 1981 on a golf course, shooting him once between the eyes, prosecutors said.

After Connolly told Bulger and Flemmi that Callahan was going to implicate them in the slaying, Martorano was sent to do away with Callahan, prosecutors said.

But one star witness did not testify -- the former FBI agent who inspired the 1997 film "Donnie Brasco." He refused to take the stand after the judge denied his request to testify anonymously.

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