The "Inside Job" Position...can be summarized thusly: the hijackers enjoyed substantial assistance, at least in the form of passive failure to take steps to stop them or actively taking steps to prevent others from stopping them (and possibly much, much worse).
Not all "Truthers" agree on all of these points, but the general consensus seems to be that:
- WTC1, WTC2, and WTC7 were not brought down by the heat of the jet-fuel fires, which had largely burned out by the time the collapses occurred, but by what appears to have been controlled demolition (a nonstandard variant thereof in the case of WTC1 and 2, but almost textbook for WTC7).
- The inability of the military to intercept in time is a huge anomaly (the lack of transponders is only a mild hinderance -- the interceptor jets never even got close to the planes due to a series of apparent "miscommunications" and other snafus), and one that has never been officially explained in any believable way -- but evidence appears to point to several deliberate delaying tactics on the part of top Bush administration officials; Rumsfeld and Cheney are heavily implicated. At the very least, someone should have lost their job -- but as I understand it, there have not even been any reprimands.
- The fact that the hijackers performed terribly in flight school and yet accomplished (on a first try!) what experienced pilots have described as a very difficult maneuver in one case -- a steep hairpin turnabout to hit the newly-reinforced side of the Pentagon, without accidentally hitting the ground -- is another huge anomaly.
- The fact that Bush deliberately ignored many warnings about an imminent attack (including a top-level briefing titled "Bin Laden Determined to Strike in US", and another showing WTC1 and WTC2 in crosshairs) -- while later claiming that "nobody could possibly have foreseen this" -- is another huge anomaly pointing at inside assistance, one of many smaller bits of circumstantial evidence (Why did Bush did not immediately evacuate from a widely-known location almost directly under the flight path of a major airport as soon as he was told of the first impact? Why did Bush and Cheney refuse -- in violation of both law and investigational procedure -- to testify on the record and separately? Why is there a pattern of orders from the White House which served to stop or hinder investigations into individuals who later became the 9/11 hijackers? There are pages and pages of such questions which I have not yet had time to catalogue.)
- The fact that evidence of this huge crime was rapidly hauled off (removed from a crime scene) and destroyed without proper investigation indicates that someone should have been indicted for obstructing investigation of a crime -- yet there have been no such indictments. Whether you agree or disagree with the official view, such obstruction is itself a crime -- and if the official view is true, proper investigation could have prevented the whole "9/11 conspiracy" meme from taking off in the first place. (It's not just the rubble from the towers that was destroyed, either; there has been extensive destruction of tape recordings and other valuable evidence which might have settled many questions definitively.)
- Circumstantial, but suspicious (and why wasn't it investigated?): There were reports of security guards entering the building over a weekend not long before 9/11, when the security cameras were off due to "maintenance" -- so the normal security records of their activities (some of which might have survived the towers' destruction, possibly confirming official explanations of their activities) did not exist. Why were the security employees not interviewed about their activities?