Occam's Razor is always helpful here. *If* you were going to fake a terrorist attack on the Twin Towers in order to justify a war (or for whatever other nefarious purpose), why put out such a complicated cover story; why not just say the terrorists blew the towers up with explosives, as indeed they had tried to before?

If there were no actual planes involved, why concoct the elaborate and not particularly helpful (to your cause) story about United 93?

And so on and so on.