I'll certainly agree that warning shots into the air aren't going to do the job here. "Shoot to kill" has always carried the connotation to me, rightly or wrongly, of "don't wound, kill" rather than "don't shoot AT them, just fire into the air so they remember you COULD. " Although we shouldn't forget that what goes up must come down (unless it's from a railgun, maybe, but even that wouldn't escape solar gravity. ) Plenty of people have received injuries of varying severity in such a way.