So this is not a crime?
"Murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war, or persecutions on political, racial or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of the domestic law of the country where perpetrated."
It seems to me that the firebombing a city or the atomic bombing of a city with the goal of annihilating its civilian population certainly counts as murder and extermination.