The homicide rate is falling, but domestic killings are not. For those who track this kind of violence, the deaths are both predictable and preventable.

Homicide rates have undergone the most striking change, with some of the nation’s 52 largest cities recording the fewest murders in half a century.

Homicides are down nearly 20 percent this year in 52 of America’s largest cities, a decline that spans both red states and blue states.