Primarily, countries should prosecute their own criminals. That's the whole sovereignty thing. If you don't, and these are international criminals, your country as a whole is what we call a state supporter of terrorism, or some such, if those international crimes have political goals and are directed against other countries and their people as a whole (and don't fit the high bar of self-defense). If the crimes are done by those in power, it's just state terrorism.

Actually, we call them "war crimes" and have done since at least WWII.

I'll rephrase my previous post for you, to make it clearer:

Lack of prosecution of high-level war criminals makes your country a state supporter of terrorism. (the claim in the post)

Because that's what US war criminal leaders do. They terrorize entire nation by threatening population's survival via destruction of all their power plants, which I assume includes nuclear fallout from their nuclear power plant.