[Tatze]

eople also made it to the roof and were awaiting helicopter evacuation

Are you sure about this? The reports Ive heard was that the door to the roof was locked to prevent suicides and such. It was also thought, after the 93 bombing, that a roof evacuation would be impractical.

[vannrox]

Correction: The roof door on one tower was locked. But apparently the other door was breached and over 20 people were on that roof. They had made a number of 911 calls and police helos were trying to figure out how to rescue them when the building collapsed. The 911 reports are very telling. One tower had reports of over 700 people trapped above the wreckage.

[Chemnitz]

I heard that too. There was a heavy door barring entry to the roof, from what I heard.