See also red chips / nanothermite.
The official story is that the effects of the plane crashes and subsequent fires somehow (and on this point the official story has changed in some places and admits to being “low likelihood of probability” in others) caused the buildings to collapse. The government has to claim this in order to blame the 3,000 or so deaths on the hijackers, and to prevent people from knowing the truth which implicates the government itself as criminals.
The Twin Towers and Building 7 were brought down using explosives in what is known in the industry as a controlled demolition. On 9/11 Dan Rather and other news anchors said as they showed the replays of the Twin Towers coming down that they looked like controlled demolitions. Rather was right, but his comments were not repeated as the official story was put in place of these honest initial observations.
Richard Gage, AIA, founder of Architects and Engineers for 9/11 Truth, has a website loaded with information in a clear presentation to show you how the Twin Towers and Building 7 showed the features of controlled demolition. See www.ae911truth.org
It’s noteworthy that the NIST (see below, separate entry) took until late 2008 to explain what happened with Building 7. Yes obviously this team of geniuses took about 7 years to think about it and come up with a plan. Then they had to change their explanation when David Chandler pointed out that Building 7 had fallen for 2.5 seconds at the acceleration due to gravity, or free fall speed.
David Ray Griffin wrote a book about this theory by NIST about what caused Building 7 to come down. They only made themselves look more like criminals and conspirators by publishing their theory.