Interesting story here that gave rise to this question.
http://uk.news.yahoo....y-bullet-1a5e080.html
How high up can a bullet go and what kind of speeds would it need to be able to enter a humans skull? Im sure that because of the light weight it couldn't enter.
Something similar was done on the Mythbusters programme called "Penny Drop" when they tested the theory whether a penny dropped from the Empire state building could kill you. These were the results.
A penny dropped from a skyscraper lands with enough force to either kill a pedestrian on the sidewalk below or embed itself into the sidewalk.
Firing a penny at terminal velocity (65 miles per hour (105 km/h)) into concrete and asphalt disks and a ballistics gel head with a human skull failed to result in any penetrations, likely because the speed is too low and a penny's mass too small. Even when fired from a rifle, the penny was unable to penetrate concrete or a ballistic gel dummy's skull. Even modifying a rifle to shoot a penny at supersonic speeds failed to cause a penetration. In comparison, a real 6.5mm bullet split the dummy skull. Visiting the Empire State Building, the likely source of the myth, they realize that updrafts and roofs of lower floors would prevent a thrown penny from reaching street level.
So this may have been an accident but I think unlikely it went up and then entered his head on its decent. Any thoughts?