In your reporting on the stories of the terrorists who piloted three of the Sept. 11 planes, what did you find most interesting, or surprising?

I think that if you follow the track of Mohamed Atta, you see the personification of a growing anger and rage among educated people in these modern Arab countries against their own leaders and against us. And you watch Atta's personal evolution, from a belief in the modernization that the Western world represents -- he's an urban planner, a developer, an architect -- into a disgust at other facets of modernization.

And one interesting aspect of it is, why did these guys get radicalized in Hamburg, Germany? We all operate from the assumption that if they could just see our world, they would all be attracted to it and they'd want to go back and replicate it one way or another in their countries, which is why they came to Hamburg.

But while they are in Hamburg, they become radicalized. They become radicalized because, No. 1, they are outsiders, and No. 2, they lose faith in modernization. They see what modern Western power is doing to their own countries, or helping to do in their own countries through what they see as corrupt or unattractive regimes, and they also see the downside of Western culture. And they feel personally alienated, they feel like outsiders. By the time Atta is done, he neither feels at home in Egypt nor in Hamburg.

You make an interesting point about the role that Hamburg played. What is it like as a city?

It combines the industrial brawn of Detroit or Pittsburgh in the old steel days, the toughness of the New York harbor, because it's a port town, and the bawdiness of New York, New Orleans, San Francisco, and the red light districts. Hamburg has got a rough, seamy side to life, in part because it's a port. You can find anything there; in terms of morals, anything goes.

And so it's the brawn and the strength and the industry that attracts these young Arabs there -- the aircraft industry, urban planning, good universities. But when they get there, it's anonymous, it's impersonal, they feel shut out, they start to band together. If they are at all attracted to Islam, particularly conservative Islam, they are horrified by the seediness, the bawdiness, the open sex that is right out there in a place like Hamburg.

This turn on modernization is absolutely critical, and I don't think people understand that -- that we [the modern Western countries] are both attractive and repulsive. Hamburg kind of combines both that attractive and repulsive element, and they don't know about the repulsive stuff before they go there. They only discover that when they get there, and if they find their niche, and their education goes well, and their position is good at home, and if they are fairly stable, then they are able to sort that out and go home and be productive citizens. But if they are somewhat unstable -- they feel alienated, they feel shut out, they are unhappy with what is going on at home -- that's a combustible combination.

Your report lays out a series of what look to be egregious U.S. intelligence failures. But can we really expect our intelligence and law enforcement agencies to have stopped a sophisticated and determined plot like this?

Well, I think the answer is yes. I think we can. And one reason for saying this is they have stopped others.

But of this magnitude? A plot this extensive?

No, but they did essentially foil what they expected would be very serious bombings at the time of the millennium in a variety of places. They caught Ahmed Ressam. And it wasn't just Ressam. There were plans for significant attacks on American and Western installations in Europe and in Jordan -- multiple attacks coordinated in multiple countries. So, they have done it.

But I think you have to give the hijackers credit for having been very smart about exploiting the weaknesses of our system: for example, immigration, the pilot training, visas. They knew we were inattentive and they exploited it to the Nth degree.

I think that if you look at the individual episodes -- the failure of the INS to stop Mohamed Atta when he's got an expired visa and he's using his visa improperly -- there's really no excuse for that.

You have this ridiculous episode at the Miami airport where they abandon a plane on the runway and it appears as though the FAA does nothing more than an absolutely cursory kind of report.

You have this arrest of Moussaoui, with alert flight instructors saying to the FBI, "Hey, this guy wants to do something that's really weird," and literally they were saying to the FBI, "Are you guys aware that a fully fueled 747 can be used by a pilot as a bomb?" They are actually prefiguring what happened. And the FBI responds locally, but they don't get the message.

If you go through each one of those episodes, you can say both that they should have spotted it and that might have thrown a monkey wrench into things. And you also can say, even if they had spotted it and did something about it, it might have disrupted things, but it wouldn't have stopped the plot. Which leads you to the greatest failure of all.

Which is?

The greatest failure of all, I think, is an intangible. It's a failure of the imagination, a failure to imagine that Al Qaeda could pull off this kind of an operation in the United States with multiple planes at multiple targets using this kind of sophisticated hijacking and then a suicide mission.

When I first started out reporting on this and talking to intelligence people right after Sept. 11, what they said at the beginning was, "We had no idea that you could motivate and maintain the motivation over a long period of time and over a long distance." What they assumed was, for example, that the USS Cole was attacked by people who were based in Yemen. So you could have your preachers, you could have your motivators, you could have your organizers there, and they could be keeping people pumped up, and then the day they went out on the suicide mission they'd go out and that was it. Same as in Palestine, or when the embassies were attacked in East Africa. The cell was operating out of Somalia and then in Kenya. So the picture that the intelligence people had was of a fairly close proximity to the cell and the terrorist. And this notion that you can operate long distance, over a long period of time, and keep people dedicated, motivated -- they simply didn't understand that there was that kind of capability.

I talked to guys inside and outside the FBI, and to others from the CIA. Essentially they said, "We could not get the FBI's attention to focus on us. And, except for a very small handful of experts, people simply couldn't comprehend that this was a danger that we had to worry about." Now, what that means then is that when the individual tickler comes in from Minnesota, with the arrest of Moussaoui, people who are in decision-making positions are not mentally preconditioned to think in terms of what happened.

So that's what I mean by a failure of imagination. The evidence comes in, but your mental reactions are not geared to thinking in these kind of terms. When the guy calls from the flight school and says they could take a 747 with fuel and plow it into a building and that's a bomb, you hear it but you say, "Ah, that's a wacko idea." You don't say, "Holy Jesus, that's what we've got to worry about."

You're actually talking about something much bigger than a kind of tactical failure, you're talking about a real cultural failure. ...

That's right, I'm talking about a cultural gap, a cultural failure, and that's why I call it a failure of imagination. It's a failure to imagine what the danger is. It's a failure of understanding the world we live in and the nature of the enemy.

After all, there had been a truck bombing at the World Trade Center [in 1993] -- so attacking the World Trade Center, nobody can say they couldn't imagine that. There had been attacks on American embassies and there had been plane hijackings. There was a guy who had been arrested in the Philippines who actually talked in 1995 -- and I know the FBI was informed about it -- and he said that he had a plan to dive a plane into CIA headquarters.

So the specific idea of using a plane against a prime U.S. government target, that was in the bloodstream. But there was a loss of institutional memory. The guys who were around and in important positions in 1995 when that [information] came in, they had left the government. I talked to the guys who were in charge under Clinton in 2000 and basically they hadn't heard it; it hadn't been passed on.

Was there one moment that you remember in reporting this story where the light bulb went on and it became clear to you that this plot should have been stopped?

There was a moment when I was talking to Bob Blitzer -- he was the FBI's chief of counterterrorism from 1996-1998. I asked him what his reaction was when he saw the World Trade buildings attacked, and this is his quote:

"When I saw those planes hit the World Trade tower, I was not surprised. The first thought on my mind was, 'My god, they finished the job.' I knew it was these guys because they are so committed, they have so much hatred of the West. Incredible determination. Incredible people."

What Blitzer got was the continuity. This didn't come out of the blue. Our failure was to think forward. What I understood from his comment was that we as a nation, and the FBI and the CIA, simply didn't understand that. And that's why we got hit.

They [the terrorists] made mistakes, and what was really stunning about their mistakes is how quick they were to correct them and how clever they are at bulling right through them and faking us out. That's really astonishing. Atta ... gets caught without a driver's license, and within 15 days every one of the hijackers in Florida has gotten a driver's license.

They are very smart. That's what makes them so formidable. They are bright, they think, they learn. And I think killing off the leadership is clearly important, but if we don't do something about our policies and if we don't do something about how we deal with that part of the world we're going to have the same problem in 10 years.