For one thing, the "wrong" leader is in the White House for this sort of thing, as far as the U.S. media are concerned. The soldiers who put underwear ont the heads of prisoners at Abu Ghraib were portrayed as war criminals by the U.S. media, while they're already reporting unsubstantiated hints about a mysterious "head injury" that this guy suffered in Iraq.
Secondly, the details of this story may well include some extremely embarrassing facts about the perpetrator's prior medical or personal history that would lead any objective observer to question why he was ever sent to Afghanistan in the first place.
And thirdly (and perhaps most important of all), there's always going to be a fear that this sort of episode is actually going to be far more effective in "winning" over in Afghanistan (whatever that is even supposed to mean) than any of the other nonsense the U.S. has been doing for more than a decade.