I've made it a point to keep a low profile concerning this Zimmerman/Martin case until more evidence came forward. According to MSN.com, an affidavidt was filed by the procecuting attorneys indicating that Zimmerman pursued Martin and confronted him, thus provoking the attack which led to Martin's death. If the allegations are true, I don't see Zimmerman being found not guilty for taking this young man's life.
You can read the affidavit here.
One thing the affidavit does make clear: Trayvon Martin was living (or more accurately visiting one of his parents; the affidavit doesn't make clear whether it was his mother or father) in the gated community Zimmerman believed him to be "casing" for a potential home invasion. The irony here is according to the affidavit, Zimmerman lived there, too.