Updated

Lawyers for gangster James "Whitey" Bulger (BUHL'-jur) say the federal government is trying to conceal the "sordid history" of Bulger's relationship with law enforcement by trying to prevent him from using his claim that he received immunity for his crimes from a former federal prosecutor.

Bulger's lawyers responded to a ruling Monday by a federal judge who said Bulger's claim that he had immunity for future crimes, including murder, "was without authorization" and is "unenforceable."

Attorneys J.W. Carney Jr. and Hank Brennan said Bulger is prepared to testify at his trial about how and why he received immunity from former federal prosecutor Jeremiah O'Sullivan. They said Bulger's right to a fair trial is at stake.

Bulger, the former leader of Boston's Winter Hill Gang, is set to go on trial in June, charged with participating in 19 murders.