In predominantly African-American neighborhoods of U.S. cities, far too many killers have gotten away with far too many crimes for far too long, fueling a disastrous murder epidemic. Solving these murders and other serious crimes of violence in black communities should be a top goal for law enforcement--and it deserves to take priority over much more widely discussed issues such as racial profiling and the excessive use of force by police in black neighborhoods, from Ferguson to Staten Island.

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But instead of checking this wave of urban violence, America threw up its hands. Prison terms per unit of crime in the U.S. hit rock bottom in the 1960s and '70s, making the U.S. one of the world's most lenient countries, as William J. Stuntz of Harvard Law School and others have shown. Reformers focused on the rights of defendants, remaining blind to the ravages of under-enforcement.

In the 1980s, a get-tough backlash hit, ushering in the current era of mass incarceration and long sentences. But unsolved homicides still piled up in black neighborhoods. Even as convicts grew old in prison, detectives remained overwhelmed by exploding street violence.