Bill, I think that will be investigated, and I HAVE heard/read people asking the same question.

This can't possibly be considered self defense. Zimmerman got out of his vehicle, even though the police dispatcher told him NOT to, and pursued Trayvon Martin. Judging by the phone call he made to the police where he talks about seeing a suspicious-looking, probably-black male and complaining about how they always get away in a pretty calm-sounding voice, I think it was possible he just wanted to force a confrontation and shoot somebody.