I know that Mr. Zimmerman was not regular police, but he was armed and he did shoot to kill in "self defense".
It has occurred to me the seventeen year old black man armed with a box of crackers was alone on a dark night, walking through a neighborhood not his own. A large person with a gun accosted him.
In his position, I personally would have assumed the worst and resisted in "self defense". The man with the gun "won".