niether iraq nor afghanistan were signatories to the geneva convention,, and the geneva conventio n makes no provisions for the mollycoddling of mercenaries or international criminals. the DOJ was well within legal boundaries to waterboard the fuck out of any un-uniformed insurgent they wished to. they also could quite legally have simply shot them like dogs as spies or saboteurs as they were not in uniform, nor were they part of any recognized military. very much like the french,, polish,, czech and italian partisans in ww2.
as to treaty violations, the US does not violate treaties. (with the exceptions of the treaties with the various native tribes of the US, which were broken before the ink was dry) we only violate agreements with indigenous populations, not internationally recognized foreign governments, that would just be rude.