pssst. Anybody can read about how to manufacture an explosive device on the internet. And the same anybody can make an attempt at constructing that device. It is the same as anybody can read about how to flay jet aircraft. Reading about it does not imply any ability to accomplish the task. This incident implies that someone that had experience in constructing HE devices, keeping them at ,umm, proper environmental conditions, deploying, arming, and detonating was involved. There is a rather limited group that posess this deployed "capability". And that group does not include despondent sophomores that get the clap and do not wanna face Julia Rottencrotch's folks. Just sayin.
The group capable of doing such things is FAR larger than you might believe. When I was a kid, I used to go to the Norwalk Public Library and pull both volumes of "The Chemistry and Technology of Explosives" from the reference shelf. Published in Krakow, Poland, IIRC. I had a copy of the Anarchist's Cookbook in the mid-70's. Found a second-hand store near my mom's place in Homeland, CA, that sold copies of the U.S. Army TM on improvised explosives. They had at least hundreds of them, priced at $3 each, about 10 or 11 years ago.