If he is a Talib fighter, then he was giving aid an comfort to our enemies. It doesn't matter if he joined up before the terrorist attack. He was still there when our boys captured him. He was inside that prison when it rioted. He may have been involved in the first U.S. casualty. It was no big secret they attacked the United States. They were proud of it and they trumpeted their victory over the great Satan. The Talibs may not have told their people all the details, but they celebrated their strike against us. There's no way he could not have known that his country had been attacked. If he was still there of his own accord, helping them, then that's a clear case of treason than I've ever heard.
I may be more liberal that you on some things, but in this case I'd sooner put a bullet in his head than give him a glass of water.
I'd give him a glass of urine then a bullet to the head. Just because I see him as a renounced US citizen who is fighting for his beliefs don't mean that I wouldn't hesitate to kill the guy for fighting the US.
Similar to the Americans that went to Germany to fight for Hitler. The had the balls to go over there and fight for their evil beliefs as opposed to the closet KKK sick @#$@#s that still stain our land with their presence. But that wouldn't mean I would cheer their death any less than a native Nazi.