Sites saw the five wounded men left behind on Friday still in the mosque. Four of them had been shot again, apparently by members of the squad that entered the mosque moments earlier. One appeared to be dead, and the three others were severely wounded. The fifth man was lying under a blanket, apparently not having been shot a second time.

One of the Marines noticed that one of the severely wounded men was still breathing. He did not appear to be armed, Sites said. The Marine could be heard insisting: “He’s f---ing faking he’s dead — he’s faking he’s f---ing dead.” Sites then watched as the Marine raised his rifle and fired into the man’s head from point-blank range.

“Well, he’s dead now,” another Marine said.

When told that the man he shot was a wounded prisoner, the Marine, who himself had been shot in the face the day before but had already returned to duty, told Sites: “I didn’t know, sir. I didn’t know.”

What's next:

The Marine who shot the man was removed from the field and returned to headquarters. The investigation will address why the wounded men were left behind for 24 hours, why four of them were shot Saturday and whether the killing observed by Sites was illegal.

The judge advocate general heading the investigation of the mosque incident, Lt. Col. Bob Miller, told NBC News that depending on the evidence, it could be reasonable to conclude that the Marine was acting in self-defense.

“The policy of the rules of engagement authorize the Marines to use force when presented with a hostile act or hostile intent,” he said. “So they would have to be using force in self-defense, yes.”

But Miller added: “Enemy combatants — in this case, insurgents — who don’t pose a threat would not be considered a hostile.”

Kevin Sites has this photo weblog (last post Nov. 12)