Khmer Rouge

Yes. Islamic State is perpetrating a genocide against Non-Muslim minorities in the territory it controls, most notably Assyrian Christians and Yazidis.

You could say not at all, but because he knew about it and had a position of authority within the government that was perpetrating the Holocaust; you could say that he holds some responsibility.

Inflicting, unleashing, or perpetrating. "To wreak" means to make something happen that causes no good, and usually implies creating disorder or disaster. "The outbreak of war wreaked havoc throughout the countryside".