Kissinger and Mussolini are different, as their crimes are both on a larger scale than what any normal criminal is capable of perpetrating due to the sheer power differential between some random bloke with a gun and somebody able to comfortably delegate their murders to millions of random blokes with guns; because they committed their crimes so openly it's absolutely clear they're guilty; and because they are so protected by the system that getting your hands on them is only possible after a political collapse that creates a lawless transitional period. The upper echelons of imperialist regimes are just entirely outside of the scale of what a criminal justice system should be designed for. Exceptional cases always make bad law. Discussions of the death penalty should be centered on somebody accused of shooting a cashier while robbing a gas station, not on somebody publicly setting entire nations on fire.