A great book on this subject is The Law of Armed Conflict and International Humanitarian Law in War by Gary Solis (related to nrsolis?) I think it's currently used as a textbook at West Point and other places. I have a copy here. Solis is a clear advocate for rules of conduct in war and for the punishment of those who break those rules but he also does not shy away from pointing out the frequent cases when, as you note, guilty soldiers on the winning side escape punishment. E.g., here is a quote from the book concerning the trial of Ernest Medina, implicated in the My Lai massacre:

The prosecution urged that Medina knew, or should have known, of the massacre, but, in addition to inciting it, he took no action either to stop it or to subsequently bring to justice those who committed crimes. “Even if he did not personally commit any crimes in My Lai, Medina clearly failed to maintain control over men under his command who were committing scores of them.”42 Despite apparently meeting the von Leeb–List standard – knew or should have known – and, for that matter, the Yamashita standard – must have known – Medina was acquitted.43 One civilian nonlawyer who viewed the trial found the case poorly prosecuted.44 Another calls it “a striking example of the extent to which a domestic . . . tribunal will devise a restricted formulation of the superior responsibility doctrine in order to avoid the prosecution of its own nationals.”45 But that ascribes a sinister motive to the court-martial that did not exist. (p.422)

http://www.amazon.com/The-Law-Armed-Conflict-International/d...

I hope this information is helpful.