Is not reporting torture you see or deduce criminal?

Just another wrinkle to the “who’s guilty” debate. Assuming you (in the armed forces) witness acts by a superior or junior (inferior?) OR can be reasonably certain that acts that amount to torture are being committed, are you obligated to report this? Is not reporting this a crime or infraction? Seems that any number of people were in a position to have known. Or are the definitions so vague that no body would challange anybody?