Likewise to what Drift wrote.
There was also wtc7 that happened to fall without being struck, plus the people that managed to escape the scene spoke about several explosions after the plane hit, apparently from levels other than where the plane hit, thought that was weird.
Theories have been floating around, that approx 1k bodies were never found or searched for, and there is a group of architects that are requesting that the investigation be re-opened, stating that the towers fell in a sort of 'controlled demolition' type of way.
Still, a sad day marked in history, I feel for those whose families have been lost, and the rescue workers that got sick from the building dust trying to save people. ]: