Actually, you can execute people on the street extrajudicially. (You should really find yourself a new copy and paste phrase because I'm going to wreck it.)
You can execute people all day long, the question is can you get away with it? If there's no witnesses and no one recording on their phone, then you can get away with it. Cops need to get smarter about what they do and where they do it and the executions will continue.