It seems that the Marines at the spot did not know those who they shot dead were captured terrorists by the US Armed Force that entered the mosque earlier. This factor would indicate the Marines might have shot these terrorists dead without the information they were captured, and misjudge that the terrorist was about to attack or detonate an explosive. In this case, it is more likely the Marines shot the terrorist for self defense.
So perhaps we should look further up to see who created this unclear situation, eh? Our goof in prisoner handling shouldn't be license to shoot a prisoner for just moving. Perhaps the man who was shot (I won't say "victim") was unconcious when they first checked, and just now became concious--if so, should he have been shot just for coming to? In that case, the problem would have been that they hadn't identified the dead well enough, earlier.
However, I'm not sure how clear the situation is. There's still not enough information out in the public realm, to my knowledge, to make a determination. The message has to keep getting out, regardless, is that the enemy is not playing by the same rules, and while we shouldn't stoop to their level, the international and domestic public should keep the terrorists' methods of false surrender, etc., in mind.