More than likely, nano-thermite was secretly known back when the Towers were built. It was mixed in with the concrete (the construction workers didn't know what they were mixing) in preparation for the day when the Towers would have to be demolished. Even the igniting charges were built in. The buildings could have been taken down at any time.
The rest of the complex buildings have nano-thermite built into them, as well. People who work in the buildings are sitting inside time bombs.