Maybe he was working for the CIA in order to gain intel on the whereabouts of OBL. Like you might find in a spy novel. So he left his Army unit and sought the Taliban. Of course, to prove his loyalty to the Taliban, he had to aid in the killing of some US service members. His dad had to play along with this whole charade. Blah blah blah.
Maybe he is from outer space. Maybe he's working for the x-files unit of the FBI.