He is an American.
He deserves a day in an American court/court marshal.
If the facts necessitate, he may deserve time in one of our military prisons.
Since no deserter post WWII has paid more than a 24 month sentence, I am guessing 5 years with the Taliban is good to go. Maybe we only count the time he was in a cage.
He was/is an American. Period. Full stop.