Whitey Bulger's immunity claim disputed BOSTON, July 10 (UPI) -- Boston mob boss James "Whitey" Bulger's claim FBI agents gave him immunity is "unsubstantiated speculation," a federal prosecutor says. The U.S. attorney's office in Boston has asked U.S. District Judge Richard Stearns to recuse himself, the Boston Herald reported Tuesday. Defense lawyer J.W. Carney, who has said he will not go into details about the supposed grant of immunity until there is a hearing, argues that Stearns, who was formerly a federal prosecutor involved in the Bulger case, must have been aware of it. Bulger and his partner, Stephen Flemmi, were FBI informants for many years, although Flemmi later said the two gave the FBI "expletive" while receiving "gold" in return. The relationship became a major scandal after Bulger disappeared and his FBI handler, John Connolly, was convicted of federal racketeering and state murder charges. Carney said in his motion he will not go into details about the immunity grant until there is a hearing. "Absent a detailed affidavit from defendant Bulger, the factual claims in defendant's motion are little more than unsubstantiated speculation," prosecutors said in their response. Bulger, who lived in hiding until his arrest last year in California, faces a long list of charges, including 19 killings.