It doesn't matter if the HVAC penthouses and the interior began "collapsing" before. That is classic controlled demolition
The fact is you have all the perimeter columns and their facades....plus whatever floors left and the FFE that defended at the speed of gravity for 100 feet.
So, 100 feet...approximately 8 stories...something had to completely disappear under these massive blocks....for it (the upper block) to descend at free fall acceleration.
The only plausible answer in known physics??
Someone or something must have simultaneously gotten rid of the same below to make that 108 foot block fall, as it did, at the speed of gravity.
No other way ofr explaining around that one.
Time to INVESTIGATE the investigators of 9/11. PROSECUTE the prosecutors. EXPOSE the cover-up.