Article 84 of the Third Geneva Convention
A prisoner of war shall be tried only by a military court, unless the existing laws of the Detaining Power expressly permit the civil courts to try a member of the armed forces of the Detaining Power in respect of the particular offence alleged to have been committed by the prisoner of war. In no circumstances whatever shall a prisoner of war be tried by a court of any kind which does not offer the essential guarantees of independence and impartiality as generally recognized, and, in particular, the procedure of which does not afford the accused the rights and means of defense provided for in Article 105.