How do you determine if the police are being successful? If there are more arrests, are they more successful? Perhaps you ask about crime statistics - but those statistics are recorded by the police. I think we all have anecdotal stories of police refusing to take police reports or saying that something is a civil matter, or simply witnessing violations of minor laws (jaywalking, littering, etc.) and doing nothing. Not only does this mean that police can very easily control crime statistics, it means that if your actual goal is preventing some specific crimes, it's not guaranteed that the police are actually working on it.
One theory is that the function of the police is to maintain order, by which is meant the status quo. Police exist to make sure that white neighborhoods don't start to feel like black neighborhoods, and that black neighborhoods don't start to feel like white neighborhoods. In that model, the two data-driven approaches (predictive policing and DICFP) fall into the same trap that any hacker on HN who has run into office politics is familiar with: the data isn't being used to decide what to do, it's being used to defend an existing decision by powerful people and argue that the decision is right. Should we keep text-based content or pivot to video? Facebook's PMs, who keep the official record of whether people watch videos, have data claiming we should pivot to video. Should we keep patrolling the same neighborhoods we've always patrolled? The police, who keep the official record of crimes, have data saying that crime is bad there.