They didn’t kill him b/c he was one of them. They didn’t know we’d bargain for him five years later. They typically kill any potential prisoners more or less immediately. I saw it a few times in Iraq, and we’re dealing with much the same kind of people in Afghanistan even if the cultural specifics are different.
That, or he was similar to "new meat" in a prison, IOW, passed around like a pack of Kools.
Bingo!
He's too old for their sexual tastes, he's beyond puberty. It's not sex.