For years, Jim Adcock, a former coroner living in the South, has been sounding the alarm to police brass and anyone else who will listen: America’s big city police departments are mired in a cold case crisis.

The national murder clearance rate – the calculation of cases that end with an arrest or identification of a suspect who can’t be apprehended – fell to 59.4 percent in 2016, the lowest since the FBI has tracked the issue.