They fear that angry opposition forces or others may kill them as soon as they are captured." This statement is merely for public consumption. The U.S. wants him dead.
Agreed, but privately, I think they want him alive for a little while so we can have a little chat with him.
Then his public capture and execution at the hands of other muslims can take place.
If he is captured alive, there will be tremendous pressure from Islamic militants in an attempt to spare his life or maybe even avoid a conviction. The sooner he dies, the better it will be to end terrorism. It would be best that he die at the hands of the Northern Alliance so that radical muslims cannot argue later that a trial was controlled by those American infidels.