I agree, and some of those have me disheartened, but that's my problem. What I want to know NELSON111 is how a pressure cooker makes a fireball. I've seen them explode on accident before. There was no fireball.
These were not simply 'pressure cooker' bombs. I don't know enough about things to know how that happened but I damn sure watched it occur.
The explosion itself looked to me like gun powder...black powder. If you had large amounts of black powder in a pressure cooker...some sort of fuse in there...like a battery...you could detonate it with a simple kitchen timer. Tape a bunch of shrapnel around it...throw some in it...and boom.
That's why I think it is domestic. Islamic terrorists usually are better at making bigger bombs.