This sounds very unlike a "terrorist cell." It sounds like two guys with very little planning going nuts for a few days. Sounds like 1,000 other stories of bad ideas you hear about from college-age kids, only most of them stop at, "Hey, let's go do this." These guys went ahead and did it, whereas most wise up and go smoke something or buy a case of Keystone Light and call it a weekend.
The plans for the bomb are online. Any one of us here could build one in a week. The more I hear about this, the more I think it's just two (or a few) guys who didn't listen to that little bit of common sense that usually shuts their Stupid down.