Man in the Middle.

In a remote jungle outpost in the Far Eastern theater of World War II, a hotheaded American soldier murders an allied British sergeant in cold blood. Stalwart American Lt. Colonel Barney Adams (Mitchum) is dispatched to defend him in the ensuing court martial. But when Lt. Adams starts encountering roadblocks in his search for evidence, and his key witnesses start disappearing one after another, he soon realizes he's merely a pawn in a mysterious conspiracy that could extend to the highest levels of military power.