Today at least, it is generally recognized that genocide is a crimen contra omnes, a crime under customary international law over which there is universal enforcement jurisdiction and responsibility. Indeed, it is commonly expected that the prohibition of genocide is a peremptory norm of customary international law, a jus cogens allowing no form of derogation under domestic or treaty-based law. It is also commonly understood that the definition of genocide contained in the Convention on the Prevention and Punishment of the Crime of Genocide defines that which is prohibited by customary jus cogens.
Jordan J. Paust,
Congress and Genocide: They're not Going to Get Away with It,
Mich. J. Int'l L.
Available at: http://repository.law.umich.edu/mjil/vol11/iss1/3