its different and has changed a few times depending on the OC, for example shooting a dicker has been legal in the past despite them not carrying a weapon.That's what the UK ROE is anyway, not so sure about OOA.
Not quite the same as shooting a 14 year old schoolgirl in the head for campaigning for education for women...
If you think about it it makes complete sense. If he is not carrying any more weapons then he is no longer a threat - killing him is entirely unnecessary and there's no reason to call it anything but murder. If he is carrying weapons, or you believe that he is still going to be a threat towards you or others then you can use controlled force to stop that happening. That's what the UK ROE is anyway, not so sure about OOA.
What a lot of people seem to want is for the ROE to be more like vengeance - "He shot at me so I get to shoot him!" - which really, really wouldn't work.
do you ever think stories like this against certain groups who are disliked by the people who tell these stories may be false?
Sounds like they shot/executed the guy after he had dropped his weapon (sorry for speculating), completely wrong and of course none of them should ever stoop to the levels of the Taliban, although it would be almost justifiable/understandable if that was the situation. Will be a very sad day if any of these Marines end up in prison.

I've watched a few vids from Apache FLIR of Taliban getting shot running away, even watched a vid where a Taliban got shot out of a tree he was hiding in. I'd link them however I doubt they're appropriate for the forum.