"Did it even matter?"
Well, if they were going to charge him with murder I think it would matter quite a bit.
My guess is the guy was dead already. An autpopsy confirmed it, so there was no way to charge the Marine. Thank goodness.
But they are still trying : "And investigators are still conducting ballistics tests to determine how the other insurgents in the mosque were killed."
From my own limited military experience, I'm going to kill anything that moves under those circumstances. If your chest is moving up and down...guess what? When it stops, the area is secure.