Updated

A lawyer for mobster James "Whitey" Bulger on Tuesday framed an attempt to get the presiding judge kicked off his client's murder case as an effort to protect the court's integrity.

"I'm not really representing James Bulger," J.W. Carney Jr. told a 1st U.S. Circuit Court of Appeals panel. "I'm representing us, the people who care about the perception of the federal prosecution system in Boston."

Bulger is the former head of the Winter Hill Gang who faces charges that he participated in 19 murders.

He fled Boston in late 1994 and was on the FBI's Ten Most Wanted Fugitives list when authorities captured him in June 2011 in California. The 83-year-old has pleaded not guilty and faces a June trial.

The defense claims U.S. District Judge Richard Stearns can't be impartial during the trial because he was a federal prosecutor in charge of the U.S. attorney's office criminal division during some of the time Bulger was an FBI informant.

But a government lawyer countered Tuesday that Stearns, who has rejected recusal appeals, didn't participate in and didn't know of any investigations involving Bulger while serving as a federal prosecutor.

Carney has said Bulger will testify at trial that the late Justice Department attorney Jeremiah O'Sullivan gave him immunity for his crimes that protected him from prosecution while he informed on the Mafia for the FBI.

But the government has said O'Sullivan, who died in 2009, testified before Congress that he didn't authorize Bulger to commit any crimes or immunize him from prosecution.

On Tuesday, Assistant State Attorney Zachary Hafer attacked the defense's failure to provide more details about the purported immunity agreement, saying there was no information about whether it was spoken or written or even the terms of the deal. He also questioned the defense's attempt to link Stearns and Bulger.

"There are no facts that support Judge Stearns' connection to the defendant in any way," Hafer said.

After a question from retired Supreme Court Justice David Souter, Carney said Bulger's immunity agreement was in place before 1984 when Stearns became criminal division chief for the U.S. attorney's office in Boston.

"That's what the evidence will show. And you're the first person to get this out of me," Carney told Souter.

Souter joined Chief Judge Sandra Lynch and Senior Judge Bruce Selya on the three-judge appellate panel.

Lynch pressed Carney for specifics, saying he hadn't provided the panel details on the type of information Stearns might have received on Bulger while at the U.S. attorney's office. Under questioning, Carney stopped short of calling Stearns dishonest and agreed he hadn't shown bias so far.

The lawyer also said the recusal motion wasn't a delay tactic and his client would be ready for trial.

But Carney said that corruption within federal law enforcement in the 1980s couldn't be ignored and not recusing Stearns would stain the integrity of Bulger's trial.

A former Boston FBI agent who provided the tip about an impending indictment that led Bulger to flee went to prison on a racketeering conviction.

And the idea of presenting a picture of fairness when it comes to Bulger's trial seemed to register with the panel Tuesday.

"I'm concerned about the public perception about whether the defendant can get a fair trial," Selya said.

But Hafer said the most relevant factor in the matter was Stearns' statement he didn't know anything about an investigation of Bulger.

"The law is clear. The facts are nonexistent and the petition should be denied," he said.

After court, the son of a man whom Bulger is accused of murdering said it might be a good idea for Stearns to be off the case.

"It's all accusations, but if this is the outcome of it, then I would like to probably see him step down," 38-year-old Boston resident Thomas Donahue said.