He may not have KNOWN, but it was definitely what he THOUGHT...<quoted text>
"Nothing"???? There had been numerous burglaries and crimes in the neighborhood during the year prior to the shooting. This is why the residents established a Neighborhood Watch. It is dark and raining. You have a person (there is no way Mr. Zimmerman could know he was a teenager) walking close to the condos in the rain. It DOES look suspicious!
If Zimmerman was just out to kill someone, why would he even bother calling 911?
"Dispatcher: How old would you say he looks?
Zimmerman: He's got a button on his shirt. Late teens.
Dispatcher: Late teens. Okay."