Cop recalls trade center explosions

Before World Trade Center 1 collapsed, a series of explosions ripped through the upper floors, according to a policeman who was at the scene on 9/11.

After WTC2 fell, says a Port Authority police memorandum dated Dec. 9, "periodically you would hear a loud boom from the top" of the north tower. The memo, signed by Officer Middleton, said that following a loud boom from upper floors was a series of smaller explosions which "appeared to go completely around the building" at upper floors.

The National Institute of Standards and Technology dealt with these smaller explosions by suggesting -- without vouching for the suggestion -- that falling debris from within the building had ejected belches of dust.

However, Middleton's account seems to indicate that the lesser explosions were loud enough to be heard from about 90 floors below.