Q - "Think Fireworks. Thwarted. Message delivered. These people are sick!"
How come the bomber was not killed?
Why wasn't the bomber blown into pieces?
Why wasn't he even bleeding?
Watching the explosion video - IMO the explosion was "Flash powder" and not a high explosive. Flash powder is used in fireworks. It will cause burns if you are too close. I also do not see any signs of shrapnel - on the bomber or the walls. From P.E., if the flash powder was in a container of PVC or "harder: like pipe, there would have been considerable shrapnel and definite lacerations to his mid-section - w/lots of blood.
Another anon mentioned the bomb being switched (Thwarted? AND Infiltrated!) Message Sent.