The only thing we know for sure is that Zimmerman's recorded discussions with 911 and even his own statements prove he was the instigator, and an aggressive one, of the incident even after 911 told him not to be and that he killed Martin. There's really isn't any ambiguity about that. From there on out it's guesswork.
Now, who started the physical altercation? No one willing to come forward knows that other than Zimmerman, who pretty was clearly determined to be provably overly aggressive in his behavior. Even IF Martin started the physical altercation (which is unknown) if an aggressive armed man is pursuing you for minor or unknown reasons (which is known by Zimmerman's own statements) by all accounts the "Stand your ground" law applies more to you than the man pursuing you.
Based on the 911 calls and Zimmerman's own statements (which show obvious aggression, prejudice statements and poor judgement) and a silent dead boy, who even by Zimmerman's own statements merely cut through a yard or two, I've got to side with Martin. You have a hot headed and armed adult instigating an altercation with a unarmed minor who has done nothing more than walk through a yard (by Zimmerman's own accounts), so maybe trespassing at worst (and I doubt even that would hold)? What sucks about the trial is that the dead boy who we have no facts about other than he cut through a yard or two, was essentially put on trial, not the man we know was the armed individtual who acted hastily and emotionally against the recommendation of 911 operators.
Now, is that 2nd degree murder? Nope. You can't prove he intended to kill Martin, there is reasonable doubt there. I really don't think Zimmerman went after Martin with the intent of killing him, but I think he is 100% responsible for creating the situation where he "had" to (according to him). That is Manslaughter. It's almost the definition of Involuntary Manslaughter (and possibly Criminal Manslaughter).
