Acting how?
Where's the indictment?...What are the charges?
When one has an enemy in his sights on a battlefield and a pull of the trigger will terminate his right to life and due process, etc., one does not say, "Shit. I sure wish I had this fucker under indictment, tried and convicted and all appellate review completed!"
Enemies in time of war do not get "due process." (Or, perhaps , to state it differently, the "process" to which they are allegedly "due" is very much different than the process a criminal defendant is entitled to receive.)
Taking up arms against the United States, terrorism, war, etc., are NOT criminal law matters to which the Bill of Rights even pertains.
Hey Achmed, you filthy motherfucker, you have the right to remain dead.