On the afternoon of Aug. 7, 2012, Greg Imhoff — a big, friendly 61-year-old construction superintendent from Madison, Wis., who had moved to Florida with his partner, Shari Telvick — went to check on the home of a neighbor.

The neighbor, Richard Detlor, was a friend, someone Imhoff had known back in Madison, where the Detlors still lived for part of the year. Whenever the Detlors went back to Wisconsin, Imhoff would look in on their house, something he did for many of his neighbors.

It is impossible to know whether, on that August afternoon, Imhoff ever saw the stranger in the house with the .22 caliber revolver; all we know for sure is that Imhoff was shot in the head. When Telvick and a friend found him that evening, he was lying in a pool of blood, dead.

The killer turned out to be a man named Billy Ray Retherford, who was on the lam after killing a woman two weeks earlier and was hiding in the Detlors’ empty home. The next day, Retherford was killed in a shootout with the police. He was using the same .22 handgun.