Hmm...something strange about this story. Lets see... assuming it didn't go in a balistic arc (which would not be possible coming straight back down) then it would have actually stopped, ran out of energy, at some altitude, maybe like 500 - 1000 feet, dpending on the caliber and round fired. Now as it's coming back down and falling at gravity's sake, it could only reach it's terminal velocity which should not be enough to penetrate someone's skull. Maybe bing them in the head pretty good. I used to know how to calculate this kinda stuff but am too lazy nowadays.
Any comments?