rogue FBI agent was responsible for the 1982 slaying of a Boston businessman, the victim's wife testified at the ex-agent's trial Monday in Miami.Former agent John Connolly, already jailed in Florida on racketeering charges, faced the first day of a murder trial in which he is accused of tipping off gangsters that businessman John Callahan was going to expose a slaying they had committed, The Boston Globe reported. Callahan's widow, Mary Callahan, called Connolly a "Judas" because he allegedly warned the mobsters Callahan was about to go to the FBI to finger them in the slaying of a Tulsa man. John Callahan's bullet-riddled body was found in a parking lot at Miami International Airport, stuffed in the trunk of a Cadillac, the newspaper said. Also to testify against Connolly, 68, is Stephen "The Rifleman" Flemmi, 74, a former Boston Mafia member and FBI informant serving a life sentence for 10 murders. Flemmi says he and James "Whitey" Bulger killed Callahan after receiving a tip from Connolly. Bulger, 79, is at large and the FBI is offering a $2 million reward for his capture, the Globe