The chief accuser of a Marine charged with murdering two Iraqi detainees took the stand once again Friday at Camp Lejeune in Jacksonville. When he did he refused to testify. Marine Sergeant Daniel Coburn invoked his right to avoid incriminating himself. Coburn's testimony earlier this week against Second Lieutenant Ilario Pantano earned Coburn scorn from other witnesses. They described Coburn as weak and bitter. Pantano maintains the April 2004 shooting of the Iraqis was in self-defense.