Actually, methinks there is a slight difference between an execution and an ill-advised (and tragic) impulse. I seriously doubt the gunners would have fired had they not thought they were firing at an armed enemy. Inexcusable for sure, but looking at the footage, I can see how they thought they were weapons. The bias of being on the lookout for the enemy probably didn't help. Someone should be and will be discharged for this, but I don't see it as an act of pure murder. I also think we need a bit more training regarding the identification of enemy combatants, but it's still tricky in the middle east since the enemy has no actual uniform that points them out.