LYNNFIELD – Lynnfield resident Arthur Gianelli, 51, was among four found guilty in Federal Court in Boston Wednesday in connection with a probe into a local racketeering, gambling and extortion ring.Gianelli is a reputed New England Mafia underboss and the brother-in-law of convicted former FBI agent and Whitey Bulger accomplice John J. Connolly Jr.A jury found Gianelli and three others guilty after a 31-day trial. Federal prosecutors said Gianelli plotted to burn down a Lynnfield sports bar, the Big Dog Sports Grille, in an attempt to intimidate the owner into selling them another bar.Also found guilty were 56-year-old Dennis “Fish” Albertelli, his wife, 54-year-old Gisele Albertelli and 64-year-old Frank Iacaboni.The case gained national profile after details of the loansharking ring were revealed.Prosecutors said Gianelli lent money through a Saugus sports memorabilia shop, Sportsworld on Route 1, and punished customers for failing to repay their debts, among them former Bruins star Gerry Cheevers.According to testimony, Cheevers, 68, borrowed cash from Gianelli through Phil Castinetti, owner of Sportsworld and apparently neglected to repay it.The delinquency brought alleged mob enforcer Phil Puopolo to the aging athlete’s door to apply pressure, according to the prosecution.The federal prosecution asserted that the syndicate loaned large amounts of money and in turn made millions of dollars in profit between 1999 and 2005. Interest rates allegedly exceeded 150 percent. The illicit business was conducted with the approval of Carmen “The Big Cheese” DiNunzio, described by the FBI as the head of organized crime in New England.Castinetti, Gianelli, his wife Mary Anne, and associate Stephen Russo in September 2006 were all named in a 520-count federal indictment charging them and nine others with racketeering, money laundering, operating an illegal gambling business, use of wire communication facilities, extortion, loansharking, arson and interstate travel in aid of racketeering.In March, Gianelli’s wife pleaded guilty to racketeering, money laundering and other charges.(Material from Item staff contributed to this report.)