I know the idea of international law is not popular in America, but please consider that the idea that non-Americans might also have rights (http://www.un.org/en/documents/udhr/), including the right not to be arbitrarily killed and the right to a trial.
Declaring that the US has the right to murder anyone at any time anywhere without trial or legal remedy is declaring war on the world.
Even if you believe in international law, that doesn't mean that U.S. courts are always the appropriate jurisdiction for contesting violations of such law. Nobody doubts federal law exists, but that doesn't mean that a state court in Kansas is the right forum for a violation of federal law that happened in Nebraska.
I don't see any reason to treat it any differently than any other unprovoked attack by one nation onto the soil of another, and take it to whatever U.N. bodies have oversight over such activities (Security Council?).
Well, that's one way you can slice it; but the UDHR and most legal traditions' understanding of human rights doesn't make that distinction in law, and I'm not sure how it's useful to this discussion here?
Declaring that the US has the right to murder anyone at any time anywhere without trial or legal remedy is declaring war on the world.