There are currently over 1,600 registered architects and engineers that have signed a petition stating that they believe the destruction of the World Trade Center Towers could have only been possible with the use of controlled explosives.
Evidence:
1) Destruction proceeds through the path of greatest resistance at nearly free-fall acceleration (in the case of WTC 7, at free-fall acceleration for 8 stories).
2) Over 100 first responders reported explosions and flashes.
3) Multi-ton steel sections ejected laterally up to 600 ft.
4) 1200-foot-diameter debris field: no "pancaked" floors found.
5) Isolated explosive ejections (squibs) 20–40 stories below demolition front.
6) Several tons of molten metal found under all 3 high-rises.
7) Evidence of thermite incendiaries found by FEMA in steel.