Trayvon Martin and Zimmerman

I see that Zimmerman is going to charged with second degree murder in the killing of Trayvon Martin. Regardless of race, it seems to me if you are armed and you instigate some kind of confrontation and an unarmed juvenile ends up shot to death then how could the shooting not be a criminal act? I am sure this will drag on for years but I think the legal system is moving in the right direction.