Better to be safe than sorry. Mr Zimmerman was performing his duty. Mr Zimmerman was armed and had every reason to believe the perpetrator was armed. One can hardly expect Mr Zimmerman to wait around while the perpetrator pulls out his gun and shoots, can one? No Zimmerman did the only rational thing he possibly could. The only person to blame here is the perpetrator - he should've stayed home where he belonged and none of this would have happened. Tragic for Mr Zimmerman to have to go through all this.

How eager they are to be slaves - Tiberius Caesar

Coulda tripped out easy, but I've changed my ways - Donovan