I believe it was a "Nova" show on PBS called "Why the Towers Fell".
Bottom line was that it had very little to do with the fire, and more to do with the type of construction used.
The WTC was built with a sturdy central core (Elevator tubes and stairwells) surrounded by a relatively thin skinned outer shell. The real culprit was the type of beam used to attach the outer skin to the inner core. These were the first items to fail and cause the catastrophic collapse. Some engineers actually said that budget constraints in the construction phase determined the type of supports used and led to the collapse.
The fact that all stairwells and elevators were concentrated at the center of the building also contributed to the low number of survivors that were caught above the impact zone. All stairwells were destroyed in building 1 IIRC, and one survived in Building 2.