// McGuinness fired, the soldiers fired back, end of. //
I suspect there's a bit more to it than that. Being a soldier, even in a combat situation, doesn't absolve you of any and all responsibilities. If for example you shoot an unarmed civilian in the back as he's running away from you, and then wander up to finish them off with a shot to the head, that's not acceptable.
That's nothing to do with this case of course, just an example. As I said, let's hear the evidence.