For generations, Black frustration with policing has been best described in a two-part statement: Cops don't care enough to solve crimes in our neighborhoods—they just come and harass our kids. Novelist Walter Mosley even built a best-selling detective series around a tough private investigator who does all the serving and protecting that cops won't do on the Black side of town.

The bitter irony is that it was this same complaint that helped spawn the aggressive policing tactics now under attack from Ferguson to New York City. In the 1980s, when crack and heroin syndicates swept through Black neighborhoods, Black parents and pastors were some of the first and loudest voices to demand a war on drugs. What they got was "broken windows" policing—an emphasis on curbing petty offenses to prevent more serious crime.

What they also got were mandatory minimum sentences for shoplifters, indiscriminate stop-and-frisk sweeps, and deadly choke holds on men selling loose cigarettes. There's little evidence that these tactics contributed much to the national decline in crime. But they did erode trust in law enforcement across many communities—leaving places like Chester increasingly bereft of the protection they badly need. With residents both fearful of police and worried about being targeted for talking to them, detectives can't find the witnesses they need to solve crimes, breeding further distrust and a vicious cycle of frustration. A 2014 New York Daily News investigation found that in 2013, police solved about 86 percent of homicides in which the victim was White. For Black victims, the number was just 45 percent. And in high-minority communities like Chester, says David Kennedy, a professor at John Jay College of Criminal Justice, clearance rates for murder—and even more so for nonfatal shootings—can get "pathetically low. They can easily fall down to single digits."