He never said a word to his girlfriend about it?
He has "defensive wounds" on his knuckles because he was running away from someone with a gun?
A very athletic 6'3" 17 year old was chased down by a 5'9" not-so-athletic 38 year old?
The list goes on.
Edit: Also, do you happen to have a source of the witness that said the screams were moving?
Listen to all of the 911 calls you will find it in one of them.