Well, a lot of people would happily tell you that war in general is murder, but killing people who aren't obviously and convincingly an immediate threat to you

Well, a lot of people would happily tell you that war in general is murder, but killing people who aren't obviously and convincingly an immediate threat to you is certainly "more murderous" than killing enemy soldiers. If the guys in the helicopter weren't soldiers, or if they were somewhere else and not Iraq, then it would legally be murder, so personally I have a hard time understanding why this is morally different. It's true that they're under a ton of pressure, and certainly they aren't totally to blame for murdering people, but it doesn't make their morally addled actions any more right. It's a shame that there is nobody who will ever answer for most such tragedies.