Jon Caruthers hypothysizes in American Thinker, Whither Osama, (article) that Osama may be hiding out in Iran and that is why we have had no major attack on US soil. Iran realizes that a major attack would attract an Iraq like repsonse and could upseat their rule, where, unlike Iraq, the citizens really do hate their leaders.

Caruthers thinks that the tribal animosities in Pakistan would create too may incentives for warring tribes to turn him over. It would be necessary to have control of access in a way that only a nation could accomplish. Iran helped Al Qaeda operatives to escape after the invasion of Afghanistan.