I have no problem believing there might have been a cover up over prior knowledge of the hijackings. The exact scope of that knowledge could be as little as knowing there will be hijackings some unknown time in the future. I believe the government may have known there would be some who were going to hijack planes at some future date and the cover up was political in nature to protect their political asses. Remember that prior to 9/11 hijackings were only to fly to a different location and demand money or to free some comrades. Prior hijackings were never used for mass murder or terrorism.

What I have a problem with is the belief that demolition charges were placed in the building prior to 9/11. The amount of people and time that would be involved in planting those charges would be entirely to large to be kept secret.