The bullet went in one side of pooor innocent li'l Trayvon, and exited, or maybe didn't exit, the other side of pooor innocent li'l Trayvon.
How do you determine whether it was travelling up or down when it struck pooor innocent li'l Trayvon?
You can see the track it took through pooor innocent li'l Trayvon, but you don't know pooor innocent li'l Trayvon's position.