For the first time, federal prosecutors in Alexandria, Va., have acknowledged that when Sami Al-Arian took a plea deal in early 2006, federal prosecutors in Tampa believed — as did Al-Arian — that it exempted him from testifying in other cases. But with this surprising admission, which begins a 24-page document filed in Virginia federal court Wednesday night, comes a provocative argument: It doesn’t matter. “The understandings of the prosecutors who negotiated that agreement … are irrelevant to (Al-Arian’s) guilt or innocence” for criminal contempt, wrote the Alexandria federal prosecutors, who maintain they are not bound by an agreement made in another district.