So even beyond that problem, how do you define a war crime/crime against humanity given a murky issue? Except it isn't as "murky" as you are making it out to be. Even if you, as an individual, don't agree with the definition of a war crime, it is codified in international law, and that's the standard that is used. In the US, war crimes are defined in Section 2441 of the US Code. In international law, they are specifically listed in Geneva II, August 1949, and Hague IV, articles 23, 25, 27, or 28. All are integrated into the US UCMJ, and I'd assume other Western nation's military law as well. All of the above constitute what the standard of judgement will be.