Born in the West End section of Boston, Massachusetts, Mercurio grew up working in the family bakery in Malden, Massachusetts. He had a fleeting resemblance to actor Dayton Callie.In 1954 at 18 years old Mercurio killed a man during a holdup in Revere Ma.He was sentenced to life in prison.In 1964 he was pardoned by Governor Volpe. After serving time in prison again,1978–86, for trying to sell 23 million dollars worth of stolen securities and also trying to take over by force a string of massage parlors, Mercurio opened an Italian food shop in the Prudential Tower in Boston. When he came out of prison Sonny was disgruntled with the Patriaca family because they didn't help his family with money while he was incarcarated.Meanwhile Winter Hill gangsters and FBI informants Whitey Bulger and Steve Flemmi, gave his girl money every week. They got along since he was the go between for Gerry Anguilo,Bostons mob boss and Winter hill. Mercurio was soon working for the Patriarca family, serving as a liaison between the family and the Irish Winter Hill Gang in Boston again.Bulger and Flemmi thought they might be able to flip him for their FBI handler John Connolly. During the 1980s, the Federal Bureau of Investigation (FBI) obtained incriminating evidence on Mercurio by electronic surveillance at his food shop. After Anguilo was sent to prison, the new leadership of Bostons mob thought they had a perfect meeting place at Mercurios shop. An underground parking garage and a freight elevator to the room where they conducted business. They figured they couldn't be followed, therefore they couldn't be bugged. The only problem was that Steve Flemmi was invited up to discuss business. He,of course, drew FBI agent Connolly a map on how to get there, so he could bug the place. The FBI had gathered enough evidence to indict Mercurio and others for extorting a couple of elderly bookmakers for a quarter of a million dollars. In order to avoid a prison term, Mercurio became an FBI informant in 1987.
Mercurio lured mobster Francis "Cadillac Frank" Salemme to a meeting in June 1989, outside a Saugus, Massachusetts International House of Pancakes restaurant, where gunmen ambushed the unarmed Salemme as restaurant patrons dining inside ducked for cover. Wounded in the chest, Salemme took cover in the restaurant's vestibule, but ran back outside to prevent bystanders from being hurt, suffering a wound to his leg.
In 1989 Mercurio informed the FBI about an upcoming family induction ceremony at a home in Medford, Massachusetts. Mercurio surreptitiously recorded the ceremony, the first time in U.S. history that a mob induction was taped. Attendees at the ceremony included Raymond Patriarca Jr., underboss Nicholas Bianco; consigliere Joe Russo; and caporegimes Biaggio Digiacoma, Vincent Ferrara, Matthew Gugleilmetti, Dennis Lepore, and Robert Carozza. While the ceremony was taking place, Mercurio even turned down the television volume in the home to improve the recording. Mercurio's recordings led to the prosecution and conviction of dozens of criminals. In 1991, Patriarca pleaded guilty to racketeering and conspiracy charges and was sent to prison for seven years. After Patriarca's indictment, Mercurio disappeared from New England to avoid indictment himself.
Angelo said he innocently met FBI Special Agent John Connolly in the Prudential Center in the fall of 1987, after Vanessa's had been searched. He was still disgruntled from the humiliation of being successfully bugged, accused the FBI of trying to "plant" evidence during their secret forays into the store and bragged that the Mafia had outsmarted them. He was trying to best John Connolly in a battle of insider information. It was a mistake. Connolly calmly rattled off the name of the Patriarca crime family's inside source for law enforcement information. Angelo had stupidly confirmed that the Patriarca crime family had a law enforcement source, and he knew what it meant if the FBI exposed his Top Echelon Informant status. Angelo's conversation earned Stephen Flemmi restored Top Echelon Informant status in November 1987. In less than a year, Angelo had joined Stephen as a Top Echelon Informant, and was constantly feeding the FBI inside information on his associates in the Patriarca crime family. In some ways he even supplanted James J. Bulger and Stephen Flemmi in importance- the FBI and the Organized Crime Strike Force were targeting the Patriarca crime family, Robert Carrozza, J.R. Russo and Vincent Ferrara, and as a member of their inner circle, Mercurio was privy to information that even Stephen Flemmi could not obtain. He threw himself into his informant role enthusiastically- even though he had been the best man at Vincent Ferrara's first wedding did not stop him from thoroughly informing on the illicit activities of his old friend. Angelo's value as an informant made protecting him a priority.
In 1994, Mercurio was convicted in Georgia of possessing 150 pounds of marijuana and was sent to prison there. He was also arrested because he tried to shoplift a $500 Shimano fishing reel in a Sandy Springs sporting goods store. He put the fishing reel in his pocket and just walked out of the store, giving the manager at the front a "Stop me, I dare you" look. The manager, a marathon runner, gave chase, and Mercurio made it about two blocks before collapsing in a breathless heap on the sidewalk. Mercurio was booked on shoplifting but released since the fake name he was using that day wasn't in the FBI national crime database. A short time later, though, he was pulled over for suspected drunk driving, and this time his fraudulent driver's license was a match. When word got back to the Boston FBI that Angelo had been arrested, FBI Special Agent Michael Buckley visited him in jail. Soon afterward, he pled guilty in the Vincent Ferrara case. The government just asked for nine years. Despite his obvious role in the attempted murder of Frank Salemme, it was significantly less time than J.R. Russo, Vincent Ferrara and Robert Carrozza received. Not only that, but federal prosecutors recommended that it be served concurrently with Mercurio's ten-year sentence in Georgia. In effect, Angelo received no jail time at all. In June 1997, Mercurio was brought back to Boston from prison in Georgia to testify in the trial of Patriarca boss Frank Salemme. His revelation in court as a government informant was a tremendous surprise to the Patriarca family. After this testimony, Mercurio was sent back to prison. In 2000, Mercurio's sentence was reduced. On his release from prison, Mercurio entered the federal Witness Protection Program and was secretly relocated to Arkansas. According to Mercurio's lawyer, Mercurio in later years felt guilty about becoming an informant and betraying the Patriarca family.
- TruTV Crime Library: Rule Returns to Boston
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- Projo.com: Mobster tells judge he informed for FBI
- Boston.com: Man who helped bug the Mafia dead at 70