A few minutes ago you didn't even know that there was a mystery and within that short amount of time you managed to solve it. Good job. The 9/11 commission could have used a regular Sherlock Holmes such as yourself.
Larry Silverstein admitted that they decided to PULL the building so that's how the script got passed around to all the networks and how they knew it was going to collapse. Or did you conveniently forget that small factoid as well?