The slope isn't that great but you are likely correct if the bullet wasn't deflected by the impact with his skull. An FMJ bullet would have zipped through his skull and should have an impact, possibly great enough, to penetrate the building some where behind him. With FMJ there would not have been a very large exit wound. A hollow point or ballistic tip would have left a hole you could almost put a fist in, and the blood would have been everywhere.