It was not the impact of the two jets that brought down the towers. These were long flight jets and each had 30,000 gallons of jet fuel in the belly. For support and weight reduction, the building floors were attached to the support columns around the perimeter of each tower. The jet fuel created a blast furnace and melted the floor attachments. First a floor dropped and landed on the floor below. Then the next did the same. Then you started the domino effect. Then the sidewalls collapsed.
This is simple physics. Bin Laden had learned (as many US engineers understand) that the fire suppression was different on the top third of the buildings. The bottom 2/3rds were covered in asbestos, a far superior insulator. So he had told the team of killers to aim at about floor 60; for maximum thermal effect.
The collapse of building 7 is had to explain. Simple cause and effect theories do not seem to apply. Which is why uneducated conspiracy merchants have a field day with the 911 tragedy. If you cannot explain the loss of building 7 then the CIA blew up the twin towers. Right? Also, the collapse of the Murrow building in Oklahoma has real conspiracy overtones, so people would suspect the government as being involved with 911.
