It was a pound(ish) quantity of C4. Which according to various bomb techs was enough to handle the room, but not much, if anything outside of it.
OMG, I just watched CNN have an expert do a re-enactment. 1 pound of C4 was applied to a wall of concrete blocks, as was the case when they killed the shooter. He never saw it coming... they killed him thru a wall, cool.
The wall was demolished, and the debris was fired over 100 yards - concrete and steel fragments became weapons that would have cut down anything human for 100 yards.
The shock wave was LESS damaging because it was outside, but inside, it would have been much greater without the open air to end it.
Cops are hella lucky the people in the building weren't killed. A pound of C4 probably leveled every room on that floor. Not a tactic I'd use regularly.