Zimmerman did nothing wrong though. He killed Trayvon but it wasn't murder. You assault a stranger you risk getting shot. He might be an asshole but he was justified in what he did.
There is a recorded 911 call of him following Trayvon in his car, being told not to confront Trayvon, and him willlfully disobeying it. That is not standing your ground.
He didn't disobey anyone. A 911 operator isn't a cop and has no authority. He was a member of the neighbourhood watch for a neighbourhood that had been burglarised multiple times before the incident. Trayvon also got away from him, decided to circle back, attack him and bash his head into the ground. That's definitely a "stand your ground" situation.