thermite/thermate seems to be a non-starter for me as the cause of the demolition of the buildings. How could it have been installed without anyone noticing?
Hatha, a couple of inches of 'fire-proof' coating (in the form of thermate) applied on the initial collapsing floors (about 10 in each building) would set the collapse in motion, once you have the momentum of the top part of the building falling at free fall speed for a couple of seconds (thousands of tons), it is mechanically impossible for the bottom floors not to start disintegrating...