Wait for the medical report.
It does not make any difference in my view. Even Zimmerman's father admits that Zimmerman was following Trayvon and trying to get an address for the police -- after the police officer on the phone told Zimmerman not to follow Trayvon.
Trayvon had the right to stand and defend himself. Zimmerman was the aggressor and did not. Zimmerman must have frightened Trayvon very much. Trayvon is the one who had the right to defend himself.
Once he called the police, Zimmerman should have just patiently waited.
There is no knowing whether Zimmerman initiated a fight with Trayvon or the other way around. There is no way of knowing whether Zimmerman slipped in the rain or whether he was hit and fell down. You have to have a trial to look at the forensic evidence -- all of it including Trayvon's injuries -- to know.