This is a case where they are at war, and, the enemy soldier was still capable of killing. there was no guarantee that he would not pick up a weapon and shoot at them, as, he was not dead. come that, he might have pulled the pin on a grenade and rolled it towards them, or, been in so much pain he would have detonated something to kill himself and other around him, yes? The fact he was still alive was a mere formality - soldiers kill soldiers all the time. if the geneva convention was more practical, it should be written by people from the field rather than pencil pushers like me, of course.
Well, cheers to the Royal Marine. I doubt the late victim was wearing a uniform and abiding by the Geneva Convention and civilized rules of war. It won't be long before the Liberals in the UK will have their troops using rubber bullets.