When you commit a crime and violate someone's freemdoms (the primary being right to life, liberty, property), you forfeit your own. When you kill someone and take their life, you steal or destroy property, you are now in debt to society. By living in a society you agree to its rules and when the rules are broken a price must be paid to deter others from breaking them.
Just because someone broke the rules, doesn't mean that everyone else gets to. The police officer was in the wrong. He was arrested, and charged. He will pay for what he did.
Be the change you want to see. Protest in a way that doesn't harm others. Many lost business and their livelihoods due to the destruction. What did they do to deserve that?