9/11 - Suspicious Evacuations and PowerDowns prior to 9/11

This video mainly discusses the fact that previous to 9/11, there have been strange evacuations and powerdowns in the top halves of the towers. in my opinion, this would be an excellent opportunity for explosives or thermite to be planted. otherwise, the towers couldnt have collapsed without the requirements for a demolition.
just think, a powerdown and evacuation. 100's, if not 1000's of workers come in. and they could have done anything, because the powerdown cut off the security cams, and the evacuation made it so that there were no witnesses. hmmm, seems like a perfect opportunity to rig a building for demolition
http://youtube.com/watch?v=nsb1R42XzMU