Why is Bridgeport, Pennsylvania so murdery?

Bridgeport is a Philadelphia suburb in Montgomery County: about 4,961 people in 0.71 square miles, six miles east of Valley Forge. It grew on flour mills, paper mills, cotton and wool mills, steelworks and brickyards, and its largest industrial park held 48 businesses. That is the kind of place the show keeps coming back to, the old mill belt round a big city, where a borough smaller than some car parks supplies a case of its own.

Four of the 17 killings within 25 miles happened in Bridgeport itself, in episode 497. The other 13 are spread across five towns, Upper Merion two miles off, Collegeville at eight, Chester at 18, Pottstown at 19 and Claymont at 22 (episodes 405, 33, 601, 637 and 422).

The cases are dated 1978, 1979, 1982, 1995, 1996, 1999, 2005 and 2013, so no single decade carries the total. Nor does one episode: episode 405 brings five victims and episode 497 four, but the other eight are spread across four more episodes. It is an accumulation, not one bad night. And it counts the show's cases, not the town's crime rate: the show picks the towns.