I'm placing this in its own thread as the 'how could they have placed bombs in the WTC buildings unnoticed' has come up several times.
There were some emergency drills before 9/11 that may have been used to place bombs throughout the building. Again from ""The Terror Conspiracy", page 49-50:
"..if there were bombs in the towers, how did they get there?
With the buildings turned to powdered ash and the metal quickly hauled away, no one will ever be certain but some interesting theories have been advanced...
..[a] theory emerged after Ben Fountain, a financial analyst who worked on the 47th floor of the South Tower, told People magazine that in the weeks preceeding 9/11 there were numerous unusual and unannounced "drills" in which sections of both towers as well as Building 7 were evacuated for "security reasons." These drills could have provided a perfect cover for persons planting explosives.
Reporting in The American Reporter, an electronic daily newspaper, Margie Burns cited President Bush's younger brother, Marvin P. Bush, as a principal in a company called Securacom that provided security for the World Trade Center, United Airlines and Dulles International Airport. The company, Burns noted, was backed by KuwAm, a Kuwaiti-American investment firm.
Securacom has since changed its name to Stratesec, but is still backed by KuwAm. Marvin Bush, who did not respond to repeated interview requests from The American Reporter, is no longer on the board of either company and has not been linked with any terrorist activities. According to its present CEO, Barry McDaniel, the company had an ongoing contract to handle security at the World Trade Center "up to the day the buildings fell down."
Many people lost their lives in the collapse of the Twin Towers because the public address system advised workers to return to their desks. Who exactly ordered that broadcast over the loudspeakers in the South Tower as workers were trying to evacute, "Remain calm, damage is in Tower One. Return to your desks."? Many people lost their lives because of these announcements. Minutes later the towers collapsed unexpectedly."