Betty Jean Ashby’s life was in danger. She knew it. Her neighbors knew it. Louisville police knew it. The man who was stalking Betty was Carl Branch, her common-law husband and the father of her four children.

When Carl showed up at her apartment on February 10, 1989, Betty climbed out a window, clad only in a shirt, and ran for her life. Carl, wielding an orange crowbar, pursued her across the street and cornered her in the bedroom of a neighbor’s apartment.

The neighbor, Marva Anderson, could only hug her four-year-old daughter and cry “Lord Jesus! Lord Jesus!” as Carl hit Betty in the head again and again until she sank to the floor, dead at age 22.

A police officer in her neighborhood had intervened on several occasions in what he called “domestic violence runs...