Later reports indicate that there were a couple of hundred IRS people in the building, but that the plane hit an unoccuppied break room, allowing just enough time for most everyone to beat feet out of the building.
Still one unaccounted for, and they still aren't giving any clues as to who, or what, that person might be.
But the fire was a real pisser. AvGas will do that.
Austin American-Statesman now reports two bodies found inside the building, one is the deceased pilot and the other apparently the “unaccounted for” person who had not been able to get out.