It was dark and raining. Nobody looked out their windows until the screaming started. So of course nobody saw the start of the altercation, only its finish.
I think there was one witness who was at the scene of the fight (but not at the beginning) who ran indoors to call 9-1-1.
I wonder what the clubhouse video shows? Could be Trayvon walking. Could be Trayvon walking right past GZ’s truck when GZ was on the phone. Could be audio of the shot fired to establish a timeline. Could be almost anything.