90% of police work is accomplished simply by being legitimate in the eyes of most people. This legitimacy is the most important resource cops possess. If they were more aware, they would guard this easily squandered wealth most jealously of all.
Police are relevant only when most people in a neighborhood will turn in criminals. If people don’t call the police, the police are blind.
When the police no longer have the consent of a neighborhood, they have failed. The next step is military occupation and a system of paid spies and informants. This sort of escalation makes an area vastly more expensive to govern until it becomes a net loss for the state.