But this is very common in Pakistan, whether its at the hands of the Army or the Police etc.
I can imagine these soldiers have seen many of their fellow soldiers being killed by the talibs, so revenge is a great motivating factor.
Another thing is that they are following orders. They are not trained to feel any sympathy for the enemy.
None of this is an excuse ofcourse.
The ultimate fault lies with their superiors. If anyone should be held accountable its them.