Why is the Chester, Pennsylvania area so murdery, by episodes?

Chester is the oldest city in Pennsylvania, founded by Swedish settlers in 1644 and renamed after an English city in 1682, when it was set aside as a haven for Quakers. It's in Delaware County, about twenty-five minutes outside Philadelphia, and it has a motto: "What Chester makes, makes Chester."

The city is in the Philadelphia commuter belt, and the ten episodes run from Chester itself out to Collegeville, twenty-four miles away, through small boroughs and townships in three states: Claymont, Wilmington, New Castle and Hockessin in Delaware, Pitman and Berlin in New Jersey, Upper Merion and Bridgeport in Montgomery County.

The cases stretch from July 1978 to February 2013, three and a half decades with no obvious cluster. The twenty-four are spread across the ten. Episode 405 has five victims and episode 497 four, but most of them have one or two apiece. That's second overall and first in the state.