On Apr 17, 11:01*pm, wrote:
Speculation is that the bombs were set off by cell phone. I wonder if
a cell signal would penetrate the metal of a pressure cooker. Mine
barely works in my metal shop building; with the doors open. Any
experts want to weigh in?

All pressure cookers have holes in the lid for both a relief valve and
the cooker's weight spike. A wire could be run out either hole for an
antenna OR some kind of external trigger, timer, radio remote, mercury
switch, whatever. A high school kid could set it up and have it work,
no special genius-level explosives knowledge needed. There's a wide
variety of possible triggers, cell phones tend to be used in the -
stans because that's the fanciest electronics most folks have access
to and they tend to be fairly cheap. Lots more possibilities here
where there are a lot more RF-controlled devices. Or there's the
classic windup alarm clock trigger.

Stan