Having seen the photos earlier, I would have no objection whatsoever if the shop owner shot Brown dead in order to protect his property.
When it comes to police enforcement in general, and specifically in this case, that justification (self-defense) is not transferable. Their job - and they are compensated by the public treasury, and far too well - is to enforce the law. No law allows for the shooting of a citizen on the street, even if he is the suspect in a crime, unless it is absolutely necessary to protect others' lives and property and the threat of imminent harm is actual.
When a cop shows up on a scene where there is no crime being committed and no warrant being served, it is absolutely unacceptable that any such situation should end in violence or death. Cops aren't allowed to cut the courts out of the decision making process. Where they do we are not living under Constitutional law.