Jesus Christ the Lord Our Saviour, you are aware that the same word can have multiple meanings, correct? We aren't talking about the dictionary definition, we are talking about the ones laid out in various international law documents, court rulings, military justice manuals, etc.
You determine what is right by holding trials, examining the evidence, and asking a jury of peers to issue a judgement, the same as you do in regular criminal justice. How is this hard to understand? These people need to be tried before the International Criminal Court, and yes, that includes various American Presidents.
http://en.wikipedia.org/wiki/Proportionality_(law)