Most crimes, fortunately, are dealt with by the several states. There is no Federal statute against murder qua murder, because that is the province of the several states. Under the strict interpretation of the Constitution most of us FReepers favor, there is no place for a general Federal statute against murder, as such a statute cannot be fitted within any of the enumerated powers of the Federal government.
I trust Arizona prosecutors will be filing an indictment for all of the murders very soon.
But they can make laws for virtually EVERYTHING else?