OK, the passengers.
There was also a fifth plane suspected of having been hijacked that day, a Delta flight. It and another plane - allegedly identified by United as Flight 93 - both landed at Cleveland after the airport was completely evacuated, in a huge hurry, on foot.
The "United 93" plane was evacuated, of 200 people, into a NASA building at Cleveland, in a very short space of time - the Delta plane landed earlier and 60 passengers were evacuated into a FAA (?) building much later.
Total passengers on the 4 hijacked planes numbered about 200...
This is all from the film and I must watch that bit again. They replayed some communication from a stewardess on 93 quite calmly saying "so-and-so is dead, oh and this person is dead, oh and that person is dead" with no background noise at all.
They also quoted one of the cellphone callers who told his mother "this is firstname lastname" (ie he quoted his surname to his own mother) and said twice "you do believe me don't you, mom?"
Also apparently cellphone calls from a high-altitude plane (which flight 93 was for a while) wouldn't have connected so all those calls must have been faked.
The implication is that the 4 planes were emptied of passengers; 2 were flown as drones into WTC, the other 2 never crashed at all, and the passengers must have been executed by the US Govt - which is the bit you really just baulk at believing - but then if it's true they effectively executed all who died at WTC.
It does sound ludicrous but maybe not as ludicrous as Bush getting elected in the first place.