The conspiracy theorists aren't talking about planting a few bombs.It's been a while, but when I visited the WTC, I remember it being pretty open. It wasn't like some top secret government installation. Thousands of people going in and out every day. How difficult would it be for a small group to slip their way in?
True, if they had to spend any length of time there, they might be noticed, but if all they had to do was plant a few bombs on a single floor, how much time would that take? If anyone asks questions, they could just bluff their way through. ("Oh, we have authorization to work here from Mr. Revoltingest." Once they hear that, then they'd say "Oh well, if Mr. Revoltingest says it's okay, then okay.")
It's controlled demolition. That typically requires structural modification,
many many explosives, & wires linking them all to a control system which
times each explosive. In much smaller buildings, this takes weeks of
work.
Maintenance staff was unaware?
Management was unaware?
Not a single tenant noticed it & complained?
They can't sell this fantasy to a commercial landlord.