The investigation done by the National Institute of Standards & Technologies into the collapse of WTC 7 on 9/11/2001 was faulty. Gravitational free-fall acceleration of the building---which NIST finally admitted after denying the possibility in its draft report---cannot occur in a fire induced progressive collapse. In their words, it is an impossibility, as it would require the removal of all supporting structure beneath.
NIST admitted that falling debris did not play a significant part in the collapse. NIST admitted that diesel fuel fires were not a factor in the collapse. Normal office fires only burned 20-30 minutes in any area. So, what caused all of the core and perimeter columns to fail simultaneously?
AE911truth.org. Watch the collapse and ask yourself if NIST makes sense.