More common in the Middle East, pressure cooker bombs like ones apparently used in Boston make for a more powerful blast.
Question: When and where did the Boston bomber or bombers acquire their pressure cookers?
New or used? Were they purchased online?
Few retail stores keep pressure cookers on their shelves. It's more typically an item that ships from a warehouse when purchased these days. And this is off season for pressure cookers, they're typically pressed into use in late summer or following fall harvest.