The bombing in 1993 was a CIA op. Financed by Khalid Mohammed under Osame Bin Laden. CIA op. For the purpose of renovating the building with demolition devises

The same people that are said to have financed the 1993 bombing are the same people blamed for 2001.

Inside job, the demolition devices were most likely planted in the building during the reconstruction from the bombing to be used on a later date.

The devises had to be strong enough to collapse the building but not so strong that they would break the 3 foot think bath tub wall of Manhattan.

It was very well planned to create the result it did. Any deviation could have flooded and destroyed Manhattan.