JEFFREY BROWN: And finally tonight, the man whose blueprint guided the 2008 terror attacks in Mumbai, India, that killed 166 people, a Pakistani-American who took the name David Coleman Headley.
He was both a paid informer for the U.S. Drug Enforcement Administration and a member of the Pakistani terrorist group Lashkar-e-Taiba.
"Frontline" and the news service ProPublica have investigated how American law enforcement and intelligence agencies missed several opportunities to thwart Headley's plot, including a tip that came from one of Headley's several Pakistani wives after the two fought.
We start with an excerpt. The correspondent is Sebastian Rotella.
SEBASTIAN ROTELLA, ProPublica/"Frontline": Her anger led to what happened next.
She goes to the U.S. Embassy in Islamabad and warns them about her husband's extremist activities just as the Mumbai plot is really gathering momentum, the reconnaissance and the preparation.
MARC SAGEMAN, former CIA official: That's right. They must have had a disagreement. She has a short fuse. She goes to denounce him and mentioned that he was trained by Lashkar-e-Taiba, he's really a terrorist. And nothing happens.
SEBASTIAN ROTELLA: Perhaps most surprising, Faiza revealed to U.S. Embassy officials that she and Headley had spent their honeymoon at the Taj Hotel the year before. In combination with her other charges, that could have led investigators directly to Headley's work for Lashkar.
Alarming and detailed accusations were piling up.
PHILIP MUDD, former FBI senior adviser: His wife says he's involved in something. You look at him for a week or a month and you can't find anything interesting. There's 72 other active investigations going on in your office. I think people are too quick in all these cases when they look at the individual case and say, hey, you should have known, when, in fact, you're not looking at an individual case.
You're looking at 6,000, saying, I can't afford to prioritize this guy, when I have got 72 other knowns that are really taking our resources and that merit further investigation.
SEBASTIAN ROTELLA: But the U.S. did collect enough intelligence to send a series of warnings in 2008 to India about a potential attack in Mumbai, including on the Taj Hotel.
G.K. PILLAI, former Indian home secretary: We got warnings that there was likely to be an attack on Mumbai. The Taj Hotel was very specific, but it's like any other thing. You put an alert, people will wait for 15 days of alert, or 30 days of alert, and then nothing happens.
SEBASTIAN ROTELLA: G.K. Pillai led the department overseeing India's security agencies. He believes that David Headley must have been a source of that information, but the U.S. never let on.
G.K. PILLAI: If the Americans had just told us once, look, we have got this guy. He's coming in. We have a little bit of a suspicion about this guy. We will just bring him to your notice. And that wasn't done.
SEBASTIAN ROTELLA: Given that you were getting these warnings, why do you think the Americans just didn't tell you about the potential danger from Headley in there period?
G.K. PILLAI: I can only say that it is because the information that David Headley was perhaps providing to the Americans proved useful enough that they were willing to overlook and keep this under wraps because he was useful to them.
JUDY WOODRUFF: Headley is now in an undisclosed federal prison, awaiting sentencing after pleading guilty to several charges.
Margaret Warner takes the story from there.
MARGARET WARNER: And ProPublica correspondent Sebastian Rotella joins us now.
SEBASTIAN ROTELLA: Thank you.
MARGARET WARNER: That's quite a fine piece of work.
Remind us how crucial David Headley was to the planning of these Mumbai attacks.
SEBASTIAN ROTELLA: He's absolutely crucial, because he does the key reconnaissance for a period of 20 months, mapping out the blueprint of the killing zone very meticulously, in-depth undercover reconnaissance, which he's able to do very effectively because he's not just a terrorist, but he's a spy.
He's being directed by the ISI, Pakistan's intelligence service. There's strong evidence to that, in addition to this terrorist group Lashkar-e-Taiba. He's essentially a joint operation. So he's working for both.
MARGARET WARNER: And he was, as your title says, the perfect terrorist. By accident of birth, he was the perfect man for the job.
SEBASTIAN ROTELLA: I think that's right. He had grown up with a foot in both of these worlds, in the U.S. and in Pakistan. He was able to sort of change shapes and change identities and function in both worlds with remarkable effectiveness.
MARGARET WARNER: And he even had -- one of your interviewers mentioned this, and you showed this -- one blue eye and one brown eye.
SEBASTIAN ROTELLA: It's sort of the classic physical symbol of that duality, yes.
MARGARET WARNER: So, after you have spent nearly two years on this project, what did your reporting lead you to in terms of what his motive was? What drove him? Was it religious zeal? Was it a hatred of India?
SEBASTIAN ROTELLA: Certainly, those two things play a role, but it's kind of a cocktail of motivations that seem to shift.
The one constant appears to be kind of a hunger for adrenaline is one of the things that people said, because, yes, the religion was important, and the nationalism, the Pakistani nationalism, was important, but this was also someone who was very Western in his outlook, who enjoyed Western culture, enjoyed the high life. So he wasn't a dour jihadi.
But the one thing that seems to be driving him, in addition to ideology and kind of glory, is this -- this adrenaline rush.
MARGARET WARNER: Now, the piece quite painfully points out at least three missed opportunities, where someone actually close to him or close to, say, his mother actually reported at least the Pakistani training camp activities to the federal authorities, either at the embassy or to the FBI.
What was your conclusion after all this as to why those weren't followed up on?
SEBASTIAN ROTELLA: That's one of the most disturbing and puzzling aspects of the case. There's really about half-a-dozen warnings, the ones we already knew about and we discovered a couple of others, where he's coming to the attention of the authorities, but for some reason he's slipping through the cracks.
There's kind of two possibilities, two scenarios. One is that it's always harder than it seems in hindsight to detect a terrorist in the making, and that the system didn't work the way it should have, that people didn't have the benefit of the previous warnings when they were investigating the next one.
MARGARET WARNER: Even though this was post-9/11.
SEBASTIAN ROTELLA: Even though this was post-9/11, and that was exactly what we were supposed to be doing, was working on those kinds of systems.
The other is this question of because he has been an informant, and because there is a sense -- there are sources who believe that he continued to do some work for some time after he was officially deactivated by the DEA in late 2001, early 2002, there's a sense that his activities or his past as an informant played a role in -- perhaps in being detected as less than a threat.
That's a very difficult area. You have people in India who go to the extreme of believing he was still a double agent all along. You have people in the U.S. insisting that that's nonsense. And then there's some evidence to suggest there may have been something in between. But we try to be very careful and balanced how we report it, because it is a profound mystery still.
MARGARET WARNER: Now, briefly -- and I don't know if you got into this -- but is this system working any better now?
SEBASTIAN ROTELLA: Certainly, you would think that it's working better than particularly some of the early warnings after 9/11. But there's still some concern, because some of these warnings were pretty recent, and you have to wonder.
One would hope so, yes.
MARGARET WARNER: Sebastian Rotella, thank you so much.
SEBASTIAN ROTELLA: Thank you.
JUDY WOODRUFF: "Frontline" airs tonight on most PBS stations.