Not a 9/11 truther, but there are some incongruities around official accounts of 9/11, for example the accounts of why CIA staffers actively blocked the FBI from being informed about the activities of future 9/11 hijackers, as discussed in the documentary "Who is Rich Blee".

There's a morass of conflicting stories, but if you're interested you could start with a close look at [1].

1: https://en.wikipedia.org/wiki/Alfreda_Frances_Bikowsky