you don't know that, so stop presenting it as fact. that is called dishonesty, and you should know better than to be dishonest.
what we do know is that a woman beating, drunk driving, police officer assaulting, gun toting man with a history of violence and snapping in anger aggressively pursued a kid walking home from the store, first by vehicle, and then on foot down a dark corridor. he was already angry, we heard him angrily proclaim how "these assholes always get away".
what happened next, we don't know, but we do know zimmerman was straddling the kid mere seconds after shooting him to death, got up, looked uninjured to everyone that saw him, and moved fluidly and alertly on film a mere 34 minutes later.