By Scott Malone
BOSTON (Reuters) - A judge said on Monday he would decide on accused Boston mob boss James "Whitey" Bulger's claim that he cannot be tried for 19 killings because former prosecutors gave him immunity.
District Court Judge Richard Stearns said there was no reason to put off a decision on Bulger's claim, noting that there would be little reason to go forward with a trial if Bulger could prove he had a valid claim to immunity.
Bulgers' lawyers request that the immunity claim be settled at trial.
"It would present a disservice to judicial economy and the orderly administration of justice to sit idly by awaiting the raising of an objection that is now ripe and which defendant has unequivocally indicated his intent to invoke," Stearns said in court papers.
Bulger was arrested in 2011 following 16 years on the run after he fled Boston on a tip from a corrupt FBI agent that arrest was imminent.
His attorneys have argued that former Assistant Attorney Jeremiah O'Sullivan gave him immunity from prosecution for crimes committed while he ran Boston's "Winter Hill" gang in the 1970s, '80s and early '90s.
Bulger, 83, has pleaded not guilty to all charges.
When prosecutors offer a suspect immunity from prosecution from a previously-committed crime, they often do so in exchange for information on a more serious offense. Bulger's attorney, J.W. Carney of the Boston law firm Carney & Bassill, said last month that his client had never been an informant.
"James Bulger was never an informant to the FBI or anyone else at any time," Carney told reporters after a hearing on Bulger's immunity claim.
He declined to say why O'Sullivan, who died in 2009, would have given Bulger immunity if not in exchange for information.
O'Sullivan in 2003 Congressional testimony, denied giving immunity to Bulger or any other members of his gang.
Assistant Attorney Zachary Hafer in a Friday court filing called Bulger's claim to have received immunity without exchanging information "strange and unsubstantiated."
Bulger's attorney had argued that deciding on his immunity claim before the trial would have unfairly limited his right to present a full defense case.
Stearns said on Monday that any grant of immunity would not have given Bulger the right to commit murder.
"Any grant of prospective immunity to commit murder was without authorization and is hence unenforceable under any circumstance," Stearns said.
Bulger's name was prominent on the FBI's "Ten Most Wanted" list for years before his arrest in California.
He faces a maximum sentence of life in prison if convicted on all charges and his trial has been scheduled to begin in June.
His case inspired Martin Scorsese's 2006 Academy Award-winning film "The Departed."
(Reporting By Scott Malone; editing by Andrew Hay)