https://youtube.com/watch?v=RLW0jKKRXMo
Go to 4:36 in the tape and replay that a few times.
He says "2 broken windows" then sounds like "boom, boom" in the background then he screams.
Interesting because :
1. if the boom was the floor above falling in on him then he would be smashed already and not able to scream.
2. He is on the 105th floor so the big collaspe was actually floors beneath him, yet if the "boom boom" was the floors beneath him collasping then he would have screamed at the same time as the boom since he is now free falling. He would have felt the floor falling before it hit below to make a boom.
3. When he does scream listen to the sound. It's rumbles and crashed like you'd expect to hear when the building is collapsing, but no more "boom, boom".
4. The booms come first then the crashing and his scream is exactly the same time as the crash.
If a "."(period) is 1/100 of a second then this is what I hear.
BOOM.........BOOM....RUMBLE-SCREAM
But doesn't it make more sense to have heard :
RUMBLE-SCREAM...BOOM...BOOM
With the boom being one floor slamming down on another.