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.