Violence breeds violence, not order. In third world countries, policemen are criminals too. My point is that things should be done in certain order or hell will break lose. Killings thief when you're off duty if there's no need for it is not how policemen should intervene. And they know that very well, but in countries like Brazil they don't care. Because in countries like Brazil (or Serbia), policemen serve the "elite" and will do everything to protect them. They don't serve people, they don't follow the law (they are the law and their actions are actions of law no matter what kind of actions those are). That is why you never hear something like this happening in developed countries, because there is law and citizens are aware of it. You also don't hear about amateur level football judges stabbing players in the chest just to be cut to pieces half an hour later by angry mob. That happens in societies where is no law, and rural Brazil is one of those.
In America they fixed this issue by letting everyone be a lawman by himself, as long he's protecting his private property. You know, Wild West and stuff like that. Their legal system is also quite different to what we have here in Europe, there have their own ways so to speak. But not how things work in civilized world