Boston mobster James "Whitey" Bulger is battling to obtain U.S. Justice Department documents that he says will prove a now-deceased prosecutor gave him immunity.

Lawyers for Bulger and Boston federal prosecutors sparred on April 26 over Bulger’s demands for information. The two-hour hearing was also about whether U.S. District Judge Denise Casper should vacate the prior judge’s ruling that the court—and not a jury—should determine whether Bulger’s alleged agreement with Jeremiah O’Sullivan gives him immunity.

Bulger is scheduled for trial in June on charges of murder, extortion, loan sharking, bookmaking, drug sales and violations of the Racketeer Influenced and Corrupt Organization Act. He appeared Friday in U.S. District Court for the District of Massachusetts wearing a fluorescent orange prison suit over a long white T-shirt.

Bulger went on the lam for 16 years after being slapped with some of the charges in 1994. The government updated the indictment after his June 2011 arrest in California.

In March, the U.S. Court of Appeals for the First Circuit granted Bulger’s petition to remove the original trial judge, Richard Stearns. Stearns held leadership posts at the Boston U.S. Attorney’s Office during the period in which Bulger has claimed immunity.

Bulger’s motions seek a wide range of documents from the U.S. Attorney’s Office and from Main Justice in Washington.

Henry Brennan, one of Bulger’s lawyers at Boston’s Carney & Bassil, said the Justice Department knew about Bulger’s and various witnesses’ criminal involvement and "they encouraged it by indifference."

Brennan then said the government "would like to package" the case as a rogue agent theory and blame former FBI agent John Connolly. Connolly was convicted in 2008 of murder, racketeering and obstruction of justice for aiding Bulger and his associates.

"You have to intervene, you have to demand that the Department of Justice be accountable," Brennan said in court.

Assistant U.S. Attorney Fred Wyshak Jr. later said the prosecutors, who claim Bulger was an informant, have produced everything from 19 related civil matters stemming from criminal prosecutions.

"The records of the Department of Justice and the FBI have been scoured for the search for the holy grail, which is supposed to be this immunity agreement," Wyshak said.

On the immunity issue, Bulger cannot be compelled prior to trial to waive his Fifth Amendment rights," according to another of his lawyers, J.W. Carney Jr. of Boston’s Carney & Bassil.

Casper asked if one of the issues was that "here there’s no sufficient proffer of what the immunity defense was" only incomplete information in the filings.

Carney replied that the defense only divulged that information "to inform our motions for discovery."

Noting Bulger’s flight, assumption of false identities and cache of guns in the California apartment where he was eventually found, Assistant U.S. Attorney Zachary Hafer said Bulger "doesn’t think he had immunity."

"If he thought he had immunity he’d move to dismiss the indictment," Hafer said.

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