HARI SREENIVASAN: Just a few hours north of me is Belgium. Authorities there were on a manhunt today for one of the suspects in the Paris attacks. They were also looking for clues, rounding up and raiding several different places at the same time.

NewsHour special correspondent Malcolm Brabant has this report from Brussels.

MALCOLM BRABANT: It was late morning when explosions erupted in the Brussels neighborhood of Molenbeek. Masked and heavily armed police surrounded the suspected hideout of a man wanted in connection with the Paris attacks.

WOMAN (through interpreter): They were in action. I saw the police rushing in. They put the barriers in place. I was wondering what was going on. Then they pushed everyone away. They asked us not to go outside.

MALCOLM BRABANT: Commandos eventually entered the besieged house through the roof, but came up empty. They'd been looking for Salah Abdeslam, a 26-year-old Frenchman living in the Belgian capital.

He's been identified as the driver of a rental car that dropped attackers off at the Bataclan concert hall in Paris on Friday night. Salah's brother, Ibrahim, blew himself up outside one of the Paris restaurants that came under assault. A third brother was one of five people arrested over the weekend in Belgium, but released.

Mohammad Abdeslam says his family is at a loss.

Mohamad Abdeslam, Brother of Salah Abdeslam (through interpreter): I cannot tell you why. I cannot tell you how they did what they did. We are an open-minded family. We never had any problem with justice. And you also must understand that, because of the tragedy, my parents are in shock, and they don't quite realize what has happened.

MALCOLM BRABANT: At least one neighbor also expressed shock, saying that she had no problems with Abdeslam.

WOMAN (through interpreter): What do I think of it? I'm sure he has nothing to do with this because I have known this kid for years. He used to play here with the youth. He's a calm boy. He didn't even smoke cigarettes. He was cool with everybody. He would always say hello, always polite, well-brought-up. I can't believe it.

MALCOLM BRABANT: There's considerable frustration here in Brussels tonight that Salah Abdeslam is still on the loose. The anguish is compounded by the fact that the police had him within their grasp, didn't realize his significance at the time, and let him go. This city is regarded as the jihadi capital of Europe, and there is an underground network that could be protecting him.

More police raids are anticipated. Two other Belgian men have been arrested and charged with being part of a terror group. All are from Molenbeek, a poor district that's home to many Muslim immigrants, and also home to several alleged terror plots in recent years.

Bilal Benyaich, a Belgian radicalism expert, says the suburb has a dark extremist underbelly.

BILAL BENYAICH, Senior Researcher, Itinera Institute: We are talking about several hundreds of people. Most of them were activated or a lot of them were activated during the Syria crisis and are fighting now or have fought in Syria. But the problem nowadays is that these radicals and that these violent extremists went rather underground.

MALCOLM BRABANT: In the Belgian Parliament, center-right opposition M.P. Georges Dallemagne blames the presence of radicalism in Brussels on hateful preaching by Saudi imams.

GEORGES DALLEMAGNE, Member of Parliament, Belgium: Since decades, there have been an active group of people coming from Saudi Arabia and who are Salifist and who have had quite a huge impact on some of the Muslims, members of Muslim community here in Brussels who have developed radical opinion and sometimes who have supported terror and violence.

MALCOLM BRABANT: What do you think Belgium needs to do now?

GEORGES DALLEMAGNE: I think, first, we have to be very drastic on people coming back from Syria. I think those people need to — not to circulate freely in Europe.

MALCOLM BRABANT: Belgium's and Molenbeek's link to the attacks also extend to the man now being called the mastermind of the plot.

Abdelhamid Abaaoud, a 27-year-old Belgian national, is believed to be in Syria. He's also been tied to an earlier train attack in France that several Americans helped thwart. Now a French police union is calling for Molenbeek to come under E.U. security control. They say the Belgian government has ceded the area to the Islamic State's control.