( CNN ) -- Reputed former mob boss James `` Whitey '' Bulger did not have the right to commit more murders after striking a purported immunity deal with the FBI in the 1970s , a federal judge ruled Monday , knocking down a key part of Bulger 's defense at his trial . Bulger , the alleged former head of Boston 's notorious Winter Hill gang , faces 19 murder charges , as well as charges including extortion , money-laundering and narcotics distribution . The defense had initially moved to dismiss the case , saying Bulger was granted immunity by federal agents working to infiltrate Irish and Italian mobs in Boston three decades ago . Judge Richard Stearns denied Bulger had `` prospective immunity '' -- that is , immunity to commit crimes made after his purported deal with the FBI . Stearns left undecided whether Bulger had `` historical immunity '' for crimes committed before a deal . He gave both sides time to review evidence on that point . Bulger 's attorneys had also sought to have a jury decide on his immunity claim , arguing he would receive a fairer hearing , but Stearns refused . Photos : Whitey Bulger in hiding . Bulger 's attorneys said he is prepared to detail the immunity deal `` for past and ongoing crimes '' at trial , and they said they will continue to fight for a jury trial . `` The federal government has done everything in its power over the past 25 years to cover up the relationship between James Bulger and federal law enforcement authorities , '' the attorneys wrote in a statement after the ruling . `` The federal government , including attorneys who worked for the ( U.S. Justice Department ) during this period , desperately want to conceal this sordid history from the jury , the victims , and the public . Today 's decision is another step toward that goal . '' The U.S. attorney 's office declined to comment . Regarding Bulger 's claim of immunity , Stearns wrote that a license to kill is `` beyond the pale and one unknown even in the earliest formalities of the common law . '' He wrote the defense has provided a `` paucity of information '' about the deal that Bulger says he struck with Jeremiah O'Sullivan , then the head of the Justice Department 's New England Organized Crime Strike Force . Prosecutors submitted an affidavit from a former U.S. Justice Department official who says that if O'Sullivan did grant Bulger immunity from his past crimes , then it was without proper approval and against agency practice . The affidavit is part of the evidence the two sides will be reviewing on historical immunity . Bulger made headlines when he was arrested in June 2011 in Santa Monica , California , after being on the run for 16 years . Before his sudden departure from Boston , he cooperated as an informant with disgraced ex-FBI agent John Connolly Jr. , who is serving a 50-year sentence for second-degree murder and racketeering . According to an indictment against Connolly filed in 2000 , Bulger became his confidential informant in fall 1975 .
NEW : Bulger 's attorneys say the federal government is covering up its role . NEW : The Justice Department declines to comment . Comment: Whitey Bulger faces 19 murder counts . A judge rules against part of his immunity claim .