He bought 200 dollars worth and it was not used in the bombs. about 2 and a half pounds total, which is not much.
The bombs used high speed military grade explosive which was obvious from the damage done as well as the lack of black powder residual on the components found. The amount of smoke was way less than you would expect, the blast fireball should have been yellow, not white (too high a temperature). The removal of limbs was due to a high speed shockwave rather than shrapnel. None of it fits black powder.
Not at all sure what explosive was used. We may never find out which is fine by me. I think the press provides entirely too much information on these types of attacks and they should just shut up.
There was lots of smoke initially, which made think it was gunpowder, not at all a military style explosive. Also one picture showed a large orange fireball, again a sign of a pyrogenic explosive, like gunpowder. If an 81mm antipersonnel mortar round had gone off in that crowded there would have been scores of people killed. Any a cellphone or pocket camera would only have captured a complete blurr.
I’m not a pyrotechnian, and will gladly defer to anyone with better knowledge, but that was my immediate impression.
All speculation at this point.
My first guess was TATP but they could have hit multiple fireworks stores and tried to keep their purchases under the radar.
BATF/FBI will eventually issue a statement on what was used. It probably will point to the fireworks as a source even if it was high grade C4.