Eye wittnesses saying it is a airplane
It was evident from the outset, looking at the wreckage on the ground, that it was an airplane, not a chopper.
I think the 'airplane' report will turn out to be the right one. Flying a copter into a building usually results in the bird ending up in a pile on the ground in the front of the building. There's usually not enough forward speed to counter the 'eggbeater' effect when the rotors hit the side of the building. Just looking at the photos, I'd say single engine small plane, probably in a stall.