Why is the Salem, New Hampshire area so murdery, by episodes?

Salem is in southeastern New Hampshire, about 35 minutes from Boston, close enough to make it a commuter suburb. It used to be part of Massachusetts. The town was settled in 1652 and spent its early years as the North Parish of Methuen until it became a New Hampshire town in 1741, and took its name from Salem in Massachusetts, not far away. Factories, tree-lined streets, lakes, arcades and dance halls gave the town a working history, and it doesn't look like a rusted factory town. The Salem area reaches further: Fremont, Epping, Wakefield, Groton, Wenham, Hampton, Deerfield and Hooksett all lie within 24 miles.

The cases run from 1964 to 2017: nine episodes, 17 murders, nine towns. No one episode accounts for all of them. Episode 656 in Groton has the most with four victims, episode 308 in Hooksett has three, three episodes have two each and four have one. The 1980s and 1990s give a steady run, the mid-2000s added several, and 2017 has the deadliest case.

The ring runs from Salem's factory past to small towns and a quiet beach town, all within reach of the centre. The Salem area is a wide commuter orbit with a long, uneven record.