Marvin Bush sat on the Board of Directors for Stratasec/Securacom which ran electronic security at the World Trade Center during the 9 month elevator renovation that was done on the buildings by Ace Elevator Co. www.usatoday.com/news/sept11/2002-09-04-elevator-usat_x.htm www.historycommons.org/entity.jsp?entity=ace_elevator_1
During this time it was not only conceivable but also reported that there were strange noisy workers inside the buildings operating on the empty maintenance floors. Look up William Rodriguez, Ben Fountain, and Scott Forbes if you need witnesses to this as well as the power down and evacuation drills being conducted the weekend before 9/11.
Rudy Giuliani's FEMA Command Bunker covers the "reconstruction" in WTC 7 and Barry Jennings is our Star Witness for what happened there.
Through the elevator shafts access can be gained to 4 foot crawl spaces between floors where explosives could have been planted without workers in the buildings realizing it or seeing what was going on. They also shifted tennants around often enough that they could hide the work from the occupancy (which was an all time low)
Technical Papers on 9/11 collapse up for peer review @ AE911truth.org