I did google it. Nothing about witnesses saying what happened. One little thing that says one 911 call may have the gunshot recorded.
Maybe somebody saw it, then we may know. But it doesn't seem unlikely that gun-toting, cop wannabe neighborhood watch captain might get a little carried away. No more unlikely than teenage kid attacking him because he was being followed.
Since this is indeed all speculative - I think it's correct to characterize the kid as doing what he thought was necessary to protect himself from some strange person who was obviously stalking him.
While Zimmerman may feel a strange black person walking down 'his' street justifies his decision to arm himself and stalk him - he completely overstepped. Hell, calling the police because he saw a black person in his neighborhood was overstepping - but everything he did afterward was so far out of bounds, it's not even on the radar.
Boiling it down to whether or not Zimmerman was then "attacked" - is moot. Zimmerman inserted himself into a situation he did not belong. There was no mention of anything that made the kid 'suspicious' other than the fact that he was walking down the street and that he was black. Neither of which rise to the level of anything.
However, anyone walking down the street who is suddenly being stalked has a right to be concerned and even justifies confronting the person who is stalking them - and even ultimately 'puffing up' to encourage said stalker to stop stalking.
What's this kid supposed to think? He's being stalked - he gives the stalker dirty looks and puffs up to hopefully make him stop - he doesn't stop? I'd think I'm in trouble - I'd do what I needed to to protect myself.
If this kid was hopping fences, running through yards, if he were carrying a weapon - any of these things could be legitimately cited as 'suspicious'. Being black and walking down the street is not - even if he was later shown to be both carrying Skittles and defending himself against what he very legitimately thought could be someone out to hurt him.
If Zimmerman isn't racist - and wasn't motivated by racist thoughts, he's clearly just plain stupid, armed and clearly dangerous - all of which I think should be enough to toss him in jail.
But that's just speculation. And while it is just speculation, it's very hard (based on what we are able to know) to assemble a scenario where Zimmerman's actions are justifiable or excusable.