aiding the enemy is pretty bad stuff But we should not be offing Americans without due process.
Everyone needs to read "Tennessee vs Garner" the Fleeing Felon case. It basically is for cops who see a felon, who is running away, and allows cops to shoot them in the back. Why? If the facts known can justify that, if allowed to escape, the person would cause imminent threats to innocent lives.
So...an American citizen, who we believe is an imminent threat to human life, who is fleeing to Afghanistan...when we find him, can we then kill him? He isnt surrendering.
Now, "imminent" is tricky. If it were Osama Bin Laden, caught on Main Street, USA, and running away, then YES, a cop could shoot him in the back. Someone that evil can be justified to be a certain threat to human life if allowed to escape.
This is the same logic the drones are for. People that are so bad, and fleeing and hiding from us, that if allowed to remain at-large, would cause absolute danger to human life. Its tricky to guess what a person MIGHT to in the future. But...if Osama Bin Laden was found in, say, Chicago, and cops let him run away and they could have shot him but instead didnt and let him escape, would that be ok?