So I was skimming into coalition transgressions during the occupation of Iraq, and ended up looking at Fallujah, 2004. One incident that caught my eye was a war crimes accusation by a correspondent that a Marine had executed a wounded, unarmed Iraqi on the ground.

On one hand, this op-ed suggests that this was a regrettable event but not a crime because the soldier made a rapid, though poor, decision under the pressure of the moment.

On the other, the embedded correspondent described the scene thus:

Code:
Platoon takes fire from mosque. Platoon assaults and takes mosque, killing 10 and wounding 5. Dead are bagged and wounded processed for extraction to the rear. Platoon moves on for the day. 
Night passes. In the morning, the platoon is informed that fire is coming from the same mosque. Platoon backtracks and investigates the mosque. 
Dead are all still there, and the same wounded as well - but one of the five is now dead, and some of the rest have fresh, bleeding, wounds. 
One of the Marines voices suspicion that one of the wounded is feigning death. Marine walks up to the insurgent, shoots him once, and walks away.
For the relevant footage of the incident, watch the last minute of the Part 1 in this link. Tell me how you see it (@spmetla), because to the untrained eye what that looks like is exactly how one would imagine a war crime against POWs transpiring. Measured, deliberate, and not an "instinctual" act in the heat of combat.

Ultimately a military investigation found no wrongdoing to pursue in the incident (apparently the same soldier shot 2 other of the wounded there as well).

Sources tell NBC News the decision was based on the fact the Marines had been warned that the enemy would feign death and booby-trap bodies as a tactic to lure Marines to their deaths. The sources said the corporal apparently feared for his life when he fired the shots.
Does that really hold up if these guys were known to have been incapacitated and secured previously, by the same unit in the same building? At the very least, where were the MPs or medics to take them away the day before?

But the investigation is not over. At least one other Marine remains under investigation for shooting the fourth unarmed insurgent in that same mosque.
I can't find anything for that investigation, but damn. 5 men captured, all dead on site within a day.

I recall from one WW2 documentary the rationalization of a German infantryman for killing a Soviet soldier during Barbarossa. German forces were advancing, and the subject came upon a Russian, whom he ordered to raise his hands. The Russian, paralyzed with fear, made no response, so after a period the German shot him and moved forward. As described that seems understandable; it could be risky to personally disarm an enemy combatant and to guard them while waiting for backup, or lead them to the rear alone. The Fallujah incident is more difficult to understand.