ROBERT SIEGEL, HOST:
The man who could provide investigators with key information about the Paris and Brussels attacks has stopped talking. Salah Abdeslam the only surviving participant in the November 13 attacks on Paris has not spoken to investigators since Tuesday's attacks at the Brussels Airport at a metro station. He's asked to be extradited immediately to France. That comes from his lawyer as Belgian authorities scramble to find other members of the terrorist cell who might still be on the loose. We're also learning more about a potential plot to build a dirty bomb. NPR's counterterrorism correspondent Dina Temple-Raston has been following all of this, and she joins us now. And, Dina, what can you tell us about the investigation?
DINA TEMPLE-RASTON, BYLINE: Well, the Belgian authorities announced that they've lowered the threat level from a four, meaning an imminent attack to a three. And I'm actually a bit surprised that they did that because investigators I've spoken with said they think there could be five to seven people who were part of this same terrorist cell who are still at large. And Belgian authorities had said publicly last week that when they arrested Abdeslam that they had identified 30 individuals who were involved with the Paris attacks. That's before the Brussels attacks even happened. They have about 18 in custody, and maybe some of the men that they were looking at had died in these latest attacks. But that still leaves a good number of suspects defined. And U.S. intelligence officials are telling me that they think they are going to be follow-on attacks.
SIEGEL: And, Dina, I'm told that you've learned some new details about the preparation ahead of the attacks. What's that?
TEMPLE-RASTON: Well, there's some evidence that this Brussels cell may have been trying to build a radiological device. Officials close to the investigation say that Khalid and Ibrahim el - sorry - Bakraoui planted a hidden camera outside the house of one of the directors of Belgium's nuclear power industry last fall. Now, NPR is holding that man's name for his safety, but during that raid late last year on an apartment rented by the el-Bakraoui brothers, Belgian investigators found 12 hours of video footage that tracked the director and his family. And officials close to the investigation tell NPR they believe the cell wanted to kidnap a member of the director's family to force him to give him what they needed to build the dirty bomb. And we just learned this afternoon that those two brothers were in fact on a U.S. terrorism watchlist, so, you know, they were known to authorities.
SIEGEL: Now, there have been reports that the bomb-maker for the Brussels attacks died in the airport attack. What have you been able to find out about that?
TEMPLE-RASTON: Well, investigators think that Najim Laachroui is one of the people who might've been building bombs. And they've been searching for him in connection with the Paris attacks for some time. And he had been linked to Abdeslam, the man who was arrested last week. Officials say that he might be one of the people in the airport surveillance photos that's been so widely distributed, and his fingers - fingerprints were found on Paris bombs and on the Brussels devices. So they suspect he either made the bombs or at least helped the bombers get them on and wire them up. But the reports of his death haven't been officially confirmed, and, frankly, if he really was the bomb-maker, it would be very unusual for him to blow himself up.
SIEGEL: Unusual because he's valuable remaining alive to the terrorists?
TEMPLE-RASTON: Exactly. You know, I know there's been a lot of discussion about how easy these TATP bombs are to make. TATP stands for tri-acetone and tri-peroxide - acetone like nail polish remover and peroxide like you'd find in hair dye. But in fact these are very, very difficult to make, and they're very volatile. And if you have a bomb-maker who can actually successfully make them, it's very important to the terrorist cell that he stay alive to make more.
SIEGEL: OK. That's NPR counterterrorism correspondent Dina Temple-Raston. Dina, thank you.
TEMPLE-RASTON: You're welcome.
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