As Raw Story notes:
A Government Accountability Office investigator smuggled live bomb components into a federal building in just 27 seconds, then assembled a bomb in a restroom and ventured throughout the building without being detected, a leaked tape revealed Wednesday.
And see this.
Indeed, as I wrote in 2005, there is substantial additional evidence that bombs could have been planted in the World Trade Center without anyone knowing:
- Bomb-sniffing dogs were inexplicably removed from the Twin Towers five days before 9/11
- The Twin Towers had been evacuated a number of times in the weeks preceding 9/11
- Workers in the Twin Towers observed heavy work taking place on supposedly empty floors in the weeks before 9-11; supposedly, the work took place on floors the elevators would not stop on without a special access key (toward the end of the video).
- There was a power down in the Twin Towers on the weekend before 9/11, security cameras were shut down, and many workers ran around busily doing things unobserved.
- Bombs could have been placed during renovation of the elevators in the Twin Towers.
- And - as an interesting coincidence - a Bush-linked company ran security at the trade centers, thus giving it free reign to the buildings
These are just a few of the known, public examples of opportunities to plant bombs. There were undoubtedly many additional opportunities available to skilled operatives. See also this video.
As with all of the other arguments trying to debunk those who question the government's version of 9/11, the argument that bombs couldn't have been planted without people observing it is incorrect.
The people still defending the government's version of 9/11 have simply not spent the time to look at the facts.