As I see it, the only thing that separates killing someone within the context of war and murder is that war is government sanctioned and approved murder which makes it "lawful" and therefore, by definition, not murder. Does the distinction matter to you? In all circumstances of war or only certain ones? Do you think that because war is government approved and sponsored, that this should absolve a soldier from the moral weight that comes with ending another person's life? I find very little to distinguish the two aside from that word "lawful".