Why did 9/11 happen? Bad intelligence.

I don't think anybody has ever satisfactorily looked into the the claims Deputy Director O'Neil made in his resignation letter. And likely, no one will ever look into what was the basis of his complaint: that investigating terrorist activity was being hampered by oil interests. Unfortunately, we can't ask him, he died on 9/11.

Everybody I know says, "Yeah, that was a failure of intelligence." And, to be sure, it was. But why? No one seems to give a damn about why that might have been. Even after the publication of O'Neil's resignation letter in which he almost foretells us of 9/11. I don't know for sure if O'Neil's claims that his anti-terror group was being told to "back off the Saudis" in the months leading up to 9/11 are true, but I damned sure think that possibility exists and that it ought to be thoroughly investigated.