LINDA WERTHEIMER, HOST:
The bombings in Brussels this past week have focused attention on the fact that Belgium has the highest number of foreign fighters in Syria of any Western European country. Hundreds have left Belgium to fight in Syria and Iraq since 2012. Many of them have returned to Belgium where they've been able to create their own terrorist networks. Pieter Van Ostaeyen, who is an independent researcher in Belgium has been tracking the flow of Belgian fighters, joins us now. Welcome to our program.
PIETER VAN OSTAEYEN: Thank you very much.
WERTHEIMER: So first of all, do we know if any of the suspects in this week's attacks had been to Syria?
VAN OSTAEYEN: We know that, for example, one of the attackers who blew himself up in Brussels Airport had been arrested at the Turkish border, possibly even twice. Unfortunately, he was sent back to Holland. And the information didn't really flow through to the Belgian security forces and hence, seems that he never returned to Holland. He was able to cross the border. And he was - he remained in Belgium completely unnoticed until he blew himself up this week.
WERTHEIMER: Do you have any idea of how many people have been to Syria and come back?
VAN OSTAEYEN: Well, according to my last count, which was in the beginning of February, we had at least 562 individuals who had been involved.
WERTHEIMER: There have been many explanations for why radicalism has rooted itself in Belgium - the divisions in the country itself, lack of communication between intelligence agencies, difficulties integrating immigrants. What do you think is the most important reason?
VAN OSTAEYEN: The main reason why so many Belgians, in the end, join the Islamic State is because we had some quite big networks involved here in Belgium. We've had Sharia4Belgium with 79 recruits. And then we've had the nucleus around Khalid Zerkani with 45 recruits. And it's especially in this latter group that we find, for example, people like Abdelhamid Abaaoud who was behind the Paris attacks, but also people who have been involved in this week's attacks in Brussels. The guys who joined these groups were able to attract other recruits just by peer pressure, social pressure. They made family, friends and relatives join the ranks of the Islamic State.
WERTHEIMER: If the Belgian authorities jump in and arrest numbers of these people, will the networks go away, or will they just re-form?
VAN OSTAEYEN: Well, this is not going to stop just by taking out the few guys who managed to escape since Paris or after Brussels. If we look at the complexity of the network and the fact that everywhere we can see more individuals linked to Abdelhamid Abaaoud, it's like a spider web. Every single point in the spider's web is connected in one way to Abdelhamid Abaaoud. It's not like they were confined cells - a cell that operated in France and a cell that operated in Brussels. No, these guys were interconnected. And I do believe, possibly, dozens more might have been involved in that particular network. And that we probably only know half about it.
WERTHEIMER: Pieter Van Ostaeyen speaking with us from Belgium. We talked via Skype. Pieter, thank you very much.
VAN OSTAEYEN: Thanks for having me.
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