One of my coworkers is also an EMT with Fairfax County fire dept. He spent the afternoon of the 11th sitting on the helipad waiting for them to bring people out so he could take them to the hospital, spent the early evening with a crew on the roof cutting air vents, then later at night went inside with a crew to serch for survivors. He got home around dawn on the 12th, slept all day, and didn't see any of the footage or get any of the details about everything that had happened until he woke up in the afternoon on the 12th and turned on the TV. The teams going inside included a structural engineer to warn them of unstable places and an FBI agent to keep an eye out for evidence that needed to be marked. He said there were lots of airliner seats scattered around the wreckage but most were empty. Makes sense considering that the terrorists herded everybody into the rear of the plane so nobody would have been strapped in, not that it would have saved them anyway.
As for the lack of wreckage and SS109s comment about the lack of damage to the Pentagon, you've got to remember that the plane didn't hit the Pentagon, it hit the concrete helipad, broke into pieces and burst into flames, and the Pentagon was hit by the bouncing plane wreckage and a tidal wave of burning jet fuel. Most of the damage to the Pentagon wasn't caused by the impact of the plane, it was fire damage caused by burning jet fuel that got into the water pipes and drain pipes so that fires kept popping up all over the place.