An airplane traveling at high speeds, impacting a stout building or the ground at a steep angle, does not leave large pieces. They're made of lightweight aluminum. Later footage showed a jet turbine I think it was... probably the most substantial part of the plane.

Mhm I watched this air on TV.

"SOME MIGHT ASK, 'HOW CAN THE SECRETARY OF DEFENSE ATTACK THE PENTAGON, IN FRONT OF ITS PEOPLE?' I SAY TO THEM, I HAVE NO DESIRE TO ATTACK THE PENTAGON ― I WANT TO LIBERATE IT!" ~ Donald H. Rumsfeld, Sept. 10, 2001

I seen something similar in Australia when it happened and was never shown again. They were showing NBC and CNN here when it happened.