MIAMI — More than 100 former FBI agents, including the one whose undercover work inspired the movie "Donnie Brasco," are fighting for the release of a colleague convicted of corruption and of helping Boston's Irish mob murder a South Florida gambling executive.

It's a long shot, and maybe the last shot, for 70-year-old John Connolly, who will spend the rest of his life in prison, barring a successful appeal.

The former G-men, who provided documents relating to the case to The Associated Press, say Connolly was prosecuted for essentially doing what his Justice Department superiors wanted: to secretly use Irish mob bosses James "Whitey" Bulger and Stephen "The Rifleman" Flemmi as informants against Italian-American gangsters in New England.

The retired agents have filed two petitions with Attorney General Eric Holder demanding appointment of a special counsel to investigate Connolly's prosecution, raising a grab-bag of claims spanning many years, some of which have been previously rejected by courts and aired in congressional hearings. They include allegations of questionable tactics by prosecutors, evidence that a key witness lied during Connolly's 2002 federal corruption trial and contentions there was a rigged result in his 2008 Florida murder case.

"I've never seen them go after a gangster like they have John," said former agent Joseph Pistone, whose infiltration of New York's Bonanno and Colombo crime families as "Donnie Brasco" in the late 1970s was made into the 1997 film starring Johnny Depp and Al Pacino.

"He was dedicated as an FBI agent. He got all kinds of commendations. All of a sudden he goes wrong? That's kind of hard to believe."

Connolly's own saga also made its way to the big screen: It formed the blueprint for the 2006 Academy Award-winning film "The Departed."

Prosecutors say Connolly permitted Flemmi and Bulger, who ran the notorious Winter Hill Gang, to commit crimes, accepted tens of thousands of dollars and other favors from them, tipped them about a pending indictment and, most seriously, passed them sensitive information about snitches in gang ranks that led to several murders. Connolly was convicted of racketeering and obstruction of justice and handed a 10-year federal prison sentence.

In Miami, Connolly was convicted of second-degree murder in the 1982 killing by a mob hit man of John Callahan, the gang-connected president of World Jai-Alai. Connolly did not have any direct role in the slaying, but was accused of tipping Flemmi and Bulger that Callahan was likely to finger them in another slaying.

So far, the Justice Department has refused to act on the ex-agents' complaints, citing Connolly's ongoing appeals of his Florida murder conviction. The ex-agents are pressing Holder to act, particularly with Connolly staring at an additional 40-year prison sentence in the Florida case that would begin as soon as his federal term ends in June.

"I feel John was wrongfully convicted," said William Reagan, a retired agent from San Francisco who posed as a long-haired radical inside the Weather Underground for eight years in the 1960s and '70s. "I don't think it amounted to a malicious prosecution. I simply think he was screwed over."

Prosecutors say Connolly is grasping at straws.

"Connolly had his trial. He got convicted. They attacked it with new evidence, and they lost that one, too," said Michael Von Zamft, an assistant state attorney in Miami who helped prosecute Connolly in the Florida case. "The concept that he is this innocent guy is just ridiculous."

Connolly, in one of several exclusive interviews with The Associated Press from a North Carolina federal prison, said his ex-FBI allies are probably his only hope.

"I'm fighting for my life here," Connolly said. "If it weren't for these ex-agents ...

"Guys who knew me know I never did any of this. I did my job."

Connolly and his allies contend he was singled out as a rogue agent responsible for mishandling Bulger and Flemmi to shield senior federal prosecutors from blame. Bulger disappeared in 1995 shortly after he and Flemmi were indicted on racketeering charges and has been on the FBI's 10 most wanted list for years.

Connolly insists he was made the fall guy because he wouldn't falsely testify that other agents were taking bribes or feeding information to the Irish gang.

"They wanted me to lie for them. I wouldn't do that," Connolly said. "The whole thing is absurd."

The former agents have no smoking gun, nothing that irrefutably proves Connolly's innocence. They provided documents about a lying witness in his first trial, government suppression of evidence and trial tactics that they say raise questions about his guilt.

The agents contend that Miami prosecutors used an improper legal maneuver to overcome a four-year statute of limitations that existed in 1982 for second-degree murder.

They persuaded a jury to discard the statute of limitations because Connolly was almost certainly armed — the presence of a firearm is a waiver to the statute — when he tipped the mobsters about Callahan's FBI cooperation. Connolly's attorneys contend the law requires that Connolly had to possess the actual murder weapon, which was impossible because he was 1,500 miles away at the time.

Connolly, however, lost his appeal in the murder case March 2; his attorney is asking for a rehearing. Absent a legal turnabout, chances are Connolly will have to report to a Florida prison after his federal term ends June 28.

Another central claim by the ex-agents is that a former New England mob boss, Francis "Cadillac Frank" Salemme, lied repeatedly during Connolly's 2002 corruption trial about Salemme's involvement in several murders. That alleged perjury became known to prosecutors in 2003, when Flemmi began cooperating and described participating with Salemme in some of the killings, but Connolly's attorneys weren't aware of it until just before his 2008 trial on the Florida murder.

During his testimony, Salemme flatly denied participating in at least four killings, such as the 1968 strangulation of crime associate Thomas Timmins in Salemme's home in Sharon, Mass.

"I have no idea ... I don't even know that he's dead," Salemme testified.

To the ex-FBI agents supporting Connolly, the suppression of the Flemmi statement is a clear violation of Connolly's rights. They also say the Justice Department should immediately renew investigations of the murders linked to Salemme, which have never been solved. Flemmi told authorities where some of the bodies are buried, but no one has attempted to exhume them.

The agents also say that the Flemmi evidence would have strengthened one of Connolly's appeals, which were based partly on a statement from a Philadelphia mobster who became friendly with Salemme in prison.

That mobster, Roger Vella, told the FBI in 2004 that Salemme bragged about how he lied to frame Connolly. Vella is identified as "CS," short for confidential source, in the FBI document.

"Salemme told the CS that he had 'spun' the prosecutors, outslicked them, and that he had been doing this for 50 years," the report says. "Salemme said he and his family had suffered for years and now it's Connolly's turn."

Prosecutors disclosed Vella's statement under seal to a federal judge and to Connolly's defense team, which used it to argue for a new trial.

A federal appeals court ruled against Connolly in 2007, and its decision suggests that Flemmi's testimony might not have swayed it. The court said the Vella evidence about Salemme's perjury wasn't enough to warrant a second trial, because it didn't go to the heart of the case against Connolly.

The fact that prosecutors held on to Flemmi's testimony for years before sharing it with Connolly's attorneys might not help him win his freedom, either.

Prosecutors are required before and during a trial to disclose to the defense any evidence that might exonerate a defendant. But after a trial, the U.S. Supreme Court has ruled that requirement is not so stringent, former Miami U.S. Attorney Kendall Coffey said.

"If they weren't aware of the information during the time of the trial, they would not be required to disclose it post trial," said Coffey, who has no connection to Connolly's case and is now in private practice. "There are a number of cases where courts have said if you look at all the other evidence, you can't find a reasonable probability that this would have been a game-changing play."

The Justice Department declined to comment on the Connolly case beyond its terse written responses to the ex-FBI agents' two petitions. The two main federal prosecutors — John Durham and Fred Wyshak — also declined to comment.

Von Zamft said the Salemme perjury evidence wasn't an issue in the Florida case because he wasn't part of that trial.

Salemme was prosecuted for lying about one of the murders and pleaded guilty in 2008 to obstruction of justice. He was sentenced to five years in prison, given credit for time served and is believed to be in the federal witness protection program. Salemme denied committing that murder in his 2008 plea agreement and only admitted he had falsely told the FBI that someone else might have been responsible.

Among the other players in this decades-long saga, Flemmi is serving a life prison sentence. Wyshak is still a Boston federal prosecutor and Durham, whose base is Connecticut, was chosen recently by President Barack Obama's administration to investigate whether harsh CIA interrogation methods amounted to crimes.