When your laws allow neighborhood watch people to carry guns then this is what you get Zimmerman is innocent according to the law and that's a good thing, people shouldn't get convicted off emotions. I'm not going to blame Zimmerman for this but i could write a long rant about what i think of laws that allow this...
Pepper spray or a tazer would be more appropriate weapons for security guards that would have just as effectively ended the confrontation, but that's a hole other topic.