A federal judge has blocked accused Boston mobster James "Whitey" Bulger’s proposed immunity defense and bid for a long list of Justice Department documents, significantly hampering his planned defense during his impending trial.

District of Massachusetts Judge Denise Casper rejected Bulger’s request that she decide before the case goes to a jury whether his purported agreement with now deceased prosecutor Jeremiah O’Sullivan gave him immunity from prosecution. Casper’s order, released on Thursday, also denied Bulger’s demands for a wide range of documents.

"[T]he Court concludes, on the present record, that there has been an insufficient proffer that any such promise of immunity was made by a person with actual authority to make it or that Bulger detrimentally relied upon such promise, or that any such agreement was enforceable as a matter of law," Casper wrote.

"Moreover, such alleged agreement, if characterized as prospective, historical or ongoing, is not a defense to be presented at trial to the jury," she added.

Bulger is scheduled to go on trial on June 10 on 19 murder charges plus counts of extortion, loan sharking, bookmaking, drug sales and violations of the Racketeer Influenced and Corrupt Organization Act.

Casper agreed with original trial judge Richard Stearns that Bulger was not entitled to have a jury decide his immunity claim. The U.S. Court of Appeals for the First Circuit removed Stearns in March due to concerns about the appearance of bias; he’d held leadership posts in the U.S. attorney’s office during the period for which Bulger has claimed immunity.

Bulger has argued that O’Sullivan gave him immunity for racketeering, extortion, money laundering and firearms offenses.

Casper wrote that Bulger could avail himself of two related defenses: the public authority defense, which covers criminal conduct done at the behest of a government official; and entrapment by estoppel, when a government official told a defendant that certain conduct was legal.

Bulger asserted during an April 26 hearing that "he does not intend to raise either defense." However, Casper gave him until May 6 to change his mind.

To make his immunity case and to challenge the credibility of various government witnesses, Bulger sought documents concerning witnesses,FBI records and more complete versions of some redacted documents already produced.

He also requested correspondence between the Boston U.S. attorney’s office and the New England Organized Crime Strike Force, which separately prosecuted organized crime during the 1970s and 1980s. He demanded each entity’s prosecution memoranda between 1967 and the present concerning any investigation of members of Bulger’s so-called "Winter Hill Gang."

Casper wrote that Bulger’s requests went beyond what case law or the Federal Rules of Criminal procedure require. "Bulger does not explain how such information constitutes exculpatory evidence or bears upon the credibility of any likely government witnesses or how it is otherwise discoverable save for the contention that it is material to his alleged defense of immunity."

According to Stephen Huggard, chairman of the white-collar practice at Edwards Wildman Palmer and former chief of the public integrity section in the U.S. attorney’s office, Casper concluded Bulger simply hadn’t made a good case for his discovery request. "I think if Bulger wanted to present more concrete evidence, she would be willing to take it," he said.

Casper also made clear that Bulger’s pre-trial testimony would not be used against him, Huggard added. Ultimately, the order "streamlines" the case, he added.

"She is doing what judges do," Huggard said. "She’s clearing away the underbrush to make sure the trial focuses on what she calls issues of guilt or innocence."

Boston solo practitioner George Gormley, whose practice includes criminal defense work, agreed. "This is going to narrow things down," he said. "Bulger, quite understandably, would prefer to have a more free flowing defense.

Bulger’s lawyer, J.W. Carney Jr. of Boston’s Carney &Bassil, did not respond to a request for comment. The Boston U.S. attorney’s office declined to comment.

Sheri Qualters can be contacted at squalters@alm.com.