Why not both? Or more?
I believe that there were Saudi terrorists trained to fly planes.
That there was explosives planted by Israeli art students.
That the towers were built as masonic symbols that were built to be destroyed.
That there were planes that took off with terrorists and passengers that ended up somewhere but not crashed into the towers or down a mineshaft in Shanksville.
That Mosad believed they were responsible. Initially.
That the CIA via OBL believed they were responsible. Initially.
That GWB believed he was responsible. Initially.
But when the space based steel atomizer ray was turned on They all learned there was a higher power, literally, that made them all feel very small.
Except whoever pulled building seven. That prick got some serious satisfaction from his work.