Most people are not even aware that a third building, WTC #7, collapsed on 9/11 at 5:20 in the afternoon. The NIST investigation atributed it to plane wreckage landing on building, a diesel tank explosion and fires.
From the recently released 9/11 photographic and video files, a new angle of WTC 7 demolition clearly shows demolition squibs (smoke from detonation charges) running the entire length of the building just before collapsing. The video also includes Silverstein's own admission of demolition, "...the decision was made to 'pull it'. So they pulled it."
At any rate, we can rule out fire, a diesel tank explosion, or plane parts as being responsible for collapsing # 7. The visual evidence, scientific evidence and Silverstein's own words are irrefutable.
We need a proper investigation into the collapse of this buiding. The 9/11 Commission did not even mention it in it's final report. The ENRON files and other on-going SEC investigation files were lost in that building when it collapsed was demolished. Possible motive?