Why is Troy, Illinois so murdery, by episodes?

Troy is in Madison County, southwestern Illinois, about 25 minutes from St. Louis. The hosts say it is more Missouri than Chicago. It began in 1819 as ten acres platted for a town and sold at $10 an acre, and it has grown into a middle-class commuter town of just over 10,000 people.

Its whole showing in the ranking is episode 140: three murders, one town, 217th overall and third in Illinois. The cases sit close together, one in 1987 and two in February 1990, so there is no long stretch of local cases to account for. Three years, three murders.

The episode opens on a 69-year-old retired janitor, a widower who had moved into a motel room after his wife died. A middle-class commuter town, then, with three murders between 1987 and February 1990 and one episode carrying them all.