I like this quote I just took from there, RE: 9/11:

"Although it wasn't completely obvious to the untrained eye at the time, WTC 7 had been seriously compromised by a 20-story gash in one corner facing Ground Zero, and by the time the evacuation order was given was visibly sagging."

In case you haven't seen it: https://www.youtube.com/watch?v=Zv7BImVvEyk