A raucous, overflow audience jeered both District Attorney Seth Williams and filmmaker Tigre Hill last night as they and two other participants conducted a firestorm debate over the Mumia Abu-Jamal case at the National Constitution Center. After it was over, lawyer and activist Michael Coard handed Hill a letter from Philadelphia lawyer David J. Wolfsohn demanding that he "immediately cease all screenings" of his new documentary about Mumia, "The Barrel of a Gun."