UPDATE: Marines try to defend the war crime:
"I would have shot the insurgent too. Two shots to the head," said Sergeant Nicholas Graham, 24, of Pittsburgh, Pennsylvania. "You can't trust these people. He should not be investigated. He did nothing wrong."
"It's all political. This Marine has been under attack for days. It has nothing to do with what he did," said Corporal Keith Hoy, 23.
Said Gunnery Sergeant Christopher Garza, 30, "He should have captured him. Maybe the insurgent had some valuable information. There may have been mitigating circumstances."
There were no mitigating circumstances, as you know if you've seen the video -- the guy was already captured, awaiting transport to military prison, wounded, and unarmed.