I think that if there is strong evidence that if anyone has committed a serious crime it should be treated seriously, and that noone should be above the law.

That is what the rule of law means. Innocent people sometimes get convicted, and guilty people sometimes escape scot free, and those are flaws on a legal system that probably can't be completely avoided. But any idea that there is some class of people who cannot be touched - that is to undermine the whole principle of the rule of law. War crimes are real crimes.