Curtailing proactive policing can reduce major crime.

Weisburd points to work by Sullivan and O’Keeffe, yielding counter-intuitive results, that "took advantage of a natural experiment in New York City that resulted from the strangling death of Eric Garner in Staten Island. Subsequent political events led to the New York City Police Department (NYPD) engaging in a ‘slowdown’ characterized by dramatic reductions in arrests and summonses. One would have expected crime to go up in this period if this type of proactivity was effective. Instead, analyzing several years of data obtained from the NYPD, they find that civilian complaints of major crimes decreased. Accordingly, they conclude that prior proactivity did not reduce crime, but led to increases in crime." Here is the Sullivan and O'Keeffe abstract:

Governments employ police to prevent criminal acts. But it remains in dispute whether high rates of police stops, criminal summonses and aggressive low-level arrests reduce serious crime1,2,3,4,5,6,7. Police officers target their efforts at areas where crime is anticipated and/or where they expect enforcement will be most effective. Simultaneously, citizens decide to comply with the law or commit crime partly on the basis of police deployment and enforcement strategies. In other words, policing and crime are endogenous to unobservable strategic interaction, which frustrates causal analysis. Here, we resolve these challenges and present evidence that proactive policing—which involves systematic and aggressive enforcement of low-level violations—is positively related to reports of major crime. We examine a political shock that caused the New York Police Department (NYPD) to effectively halt proactive policing in late 2014 and early 2015. Analysing several years of unique data obtained from the NYPD, we find that civilian complaints of major crimes (such as burglary, felony assault and grand larceny) decreased during and shortly after sharp reductions in proactive policing. The results challenge prevailing scholarship as well as conventional wisdom on authority and legal compliance, as they imply that aggressively enforcing minor legal statutes incites more severe criminal acts.