Creative Speculation

...who put together the time-line models of the fires within the buildings. He showed a film of this building suddenly collapsing behind a reporter conducting an interview. Very strange, the building just starts to disappear from the top down, collapsing in on itself.

He explained the dynamics. This building was very odd-shaped and the section that started the collapse was basically held up by one central steel pillar. As the fires inside successively ignited, flared up, and and diminished over a long period of time, the sections of the pillar were successively heated and cooled. The expansion and contraction caused the pillar to warp and "walk" over its base, a concrete pad. Eventually, it slipped off the edge of the pad, and the section it was holding up, starting at the penthouse on the top, came down, caving in upon itself. This destabilized the whole structure.

Normally office fires are put out relatively quickly and don't spread around inside a building. Due to the emergency surrounding the area, there was no attempt to put out the fires in this building and they just kept burning and spreading.