If we exclude the OCT, which I think is full of holes, then we have three options:
(1) MIHOP - I'm not a fan of plane swapping, pods, etc., but there's a possibility that, say, a governmental agency wanted to LIHOP but realised the pilots weren't much cop, so it provided them with extra flight training on the sly;
(2) LIHOP;
(3) Sub-LIHOP. For example, the CIA knew more about the hijackers than they were letting on, but actually they were trying to double some of them and the hijackers outfoxed them.
I keep changing my mind, but I think I'll go for (3) today. There was actually an attempt to double a member of the Hamburg cell (Darkazanli), so why wouldn't they try again in the States? Also, the story with the petty thief and Darkazanli's documents indicates the CIA was doing something illegal in Hamburg it didn't tell the Germans about. AFAIK the CIA wouldn't operate illegally in Germany if it wasn't quite a big deal. There is some "expert" support for this, which I have a look at here:
http://journals.democraticunderground.com/KJF/19The mains problems I have with the OCT (regarding the US inteligence community being as stupid as they allegedly were) are:
(1) There is a threshhold at which I stop believing that known terrorists could commit a terrorist act. In the London bombings, we were looking at a couple of people whose names had been mentioned in a phone call and a phone number of a third bomber; this is fine by me. In the case of 9/11 intelligence agencies knew the names/phone numbers/details of several, perhaps even most of the hijackers (based merely on what we know now - there could well be more) and the CIA had even conducted a major operation against some of them. This is just too much for me to swallow.
(2) Al Mihdhar says he was followed.
(3) Rumsfeld was told on 9/11 that 3 of the American 77 hijackers had been followed "since millenium and Cole".
(4) The NSA was obviously tapping some of their calls.
(5) The way Able Danger was shut down.
(6) The CIA front company operating out of the same hangar as Huffman.
(7) The attempt to double Darkazanli and the mysterious/comic way his documents showed up.
(8) How can Al Mihdhar get another Saudi passport if they already knew he was a terrorist? The Saudis don't give passports to known terrorists; they have a list called "known terrorists who can't get a passport".
(9) Jarrah's stop in Dubai.
(10) According to 9/11 staff director Eleanor Hill, the hijackers were "right in the centre of the FBI's counterterrorist coverage".
(11) The CIA got Al Shehhi's phone number in 1999.
(12) The way the 9/11 Commission glosses over all of this. There's no mention of Able Danger, Volz, Britannia Aviation, the UAE/US dispute over Jarrah (they just mention he was stopped, omitting the UAE claims), they didn't see the NSA intercept transcipts, there's a million things left out.
There's a little but more, but that's plenty for me to say the CR is a whitewash and there's lots we aren't being told.