This case is so troubling. We may never know for sure what really happened in the lead-up to the shooting. Trayvon's walking through the complex certainly wasn't against the law. Zimmerman's following TM wasn't against the law. Disregarding a dispatcher's statement that "We don't need you to [follow TM]" wasn't illegal, either.
Based only on the little we've learned so far, it doesn't appear either of the two committed a crime prior to the physical altercation. So at what point did one of them first commit a criminal act and who committed it? Did Zimmerman chase Trayvon down and start a physical fight with him? Did Trayvon get angry that Zimmerman was following him around and confront him, possibly socking him in the nose and starting the actual physical altercation?
I am heartbroken for Trayvon and his family, but I have to reserve judgment for now about whether Zimmerman is guilty of second degree murder.
There's no doubt this wouldn't have happened if GZ had not been carrying and if he'd just gone to his car and waited for police, but neither of those acts was illegal. The state is going to have to meet the burden of proof for M2. Can they definitively show that GZ instigated the physical contact and acted with implied malice/depraved indifference or disregard to human life? It's quite a hurdle, IMO.
We may not know much more til trial. Despite the Sunshine Law, I'm afraid there might be successful motions for some of the discovery in this case to be heavily redacted or sealed. I really don't see how anyone can be certain enough right now to make a judgment one way or the other (I'm talking strictly the legal points for M2, not the moral issues - they don't always mesh).