Federal prosecutors said Friday that James “Whitey” Bulger’s calls for the judge overseeing his trial to step aside because of an apparent bias is without merit, and they urged a federal appeals court to reject the request.

Bulger’s lawyers had asserted that US District Court Judge Richard G. Stearns has a conflict of interest in overseeing the long-awaited trial, because he was a federal prosecutor during much of Bulger’s alleged reign of terror, and so he would have known of an immunity agreement that Bulger says he had with the FBI.