Interview with Former FBI Agent Ali Soufan: "We Did Exactly What Al-Qaida Wanted Us to Do" - SPIEGEL ONLINE - News - International:
"SPIEGEL: As you explain in your book, you are convinced that 9/11 might have been stopped if there had not been the so-called "Chinese wall" between the CIA and the FBI.

"Soufan: We always worked together. We worked together during the East Africa embassy bombing. We had a great relationship. But suddenly that wall appeared due also to the misunderstanding of new guidelines organizing the relationship of intelligence and law enforcement. Unfortunately that directly contributed to the lack of knowledge about 9/11. We had actionable intelligence we transferred to the CIA but there was no follow-up.

"SPIEGEL: What kind of information was that?

"Soufan: We were investigating the Cole incident in Yemen. And we had a person who participated in blowing up the ship -- killing 17 sailors, injuring 39 -- tell us he delivered money to a main al-Qaida guy. So people who were involved in the Cole incident delivered money to two people who later flew a plane into the Pentagon. People in our government knew that these two people were in the United States, in San Diego. So, when you're doing an investigation and almost a year before you know about people moving and money and meetings, I think you have to understand that there are some limits to the wall. We had the lead, the CIA knew the identity of the two in San Diego but they did not put them on a no-fly list, they did not communicate their names to the State Department so that their visa would not be renewed."

I don't understand how "We had actionable intelligence we transferred to the CIA but there was no follow-up" is somehow evidence that the "wall" between the FBI and CIA prevented us from stopping the attacks. Apparently all you need to do to breach this impregnable wall is "transfer" the information you have to the other agency. Sounds to me like the problem was not that the FBI couldn't get information to the CIA, it was the fact that the CIA was incompetent.