This NY Times article describes the American captured by the Northern Alliance: http://www.nytimes.com/2001/12/04/national/04WALK.html
The description of him as a quiet kid obsessed with various religions in his teenage years before choosing Islam (to the exclusion of any usual teenage interests) made me think he might fit the pattern of a budding schizophrenic.
It occured to me that such an intelligent person who realized there was something “different” about him might try to solve the problem on his own with such a religious search. Then there are the current pictures of him that give me the feeling that I am looking at the flat affect of insanity.
Since schizophrenia commonly emerges in the late teens and early 20’s, I think this might be a plausible scenario to explain his actions. This would not be good news for his family, of course. When I worked in a major substace abuse treatment center it was not unusual for parents to call about a bright kid who went off to college and came back a year later with his first psychotic break. They would often be desperate for us to diagnose it as a drug problem since the truth was too awful to accept.
Obviously, I don’t have enough information to be sure about this, so I’m wondering if this theory seems reasonable to anyone else.