Molenbeek has long provided a haven for aspiring and returning foreign fighters. City officials have long ignored the suburb, leaving some returning fighters free of significant surveillance, a government official who requested anonymity told Al Jazeera. He added that in some pockets of Molenbeek more than 80 percent of the population is Muslim, and many live near or below the poverty line.

Molenbeek is a “problem," according to Jan Jambon, Belgium’s internal affairs minister. On Sunday he told the TV news show De Zevende Dag: “We don’t have control over the situation there. We need to step up our game.” He blamed a persistent neglect of the neighborhood by city politicians, who he said often turned a blind eye to social ills in the suburb.

French media over the weekend dubbed Molenbeek the European capital of “terrorism.”

Abdelhamid Abaaoud, a fugitive who is the subject of a massive search, was raised in Molenbeek and allegedly joined armed groups in Syria. Believed to be the mastermind of the Paris attacks, Abaaoud was also linked to a foiled attack plot in Verviers in January, when two policemen were killed in a shootout in the city.

Bilal Hadfi, believed to be a suicide bomber who struck near the Stade de France national stadium in Paris on Friday, was also raised in Molenbeek, according to Belgian newspaper De Standaard.

Mehdi Nemmouche, a Frenchman blamed in an attack that killed three people at the Jewish Museum in Brussels in May 2014, reportedly bought his guns in Molenbeek. So did Amedy Coulibaly, who killed four people in a Jewish supermarket in January this year on the day of the attacks in Paris on the offices of satirical magazine Charlie Hebdo.

Among Western European countries, Belgium is believed to have the highest number of foreign fighters per capita in Syria. About 200 remain in the Mideast conflict, according to Jambon, who recently said that about 130 fighters have returned to Belgium. Jambon said it is “impossible” to keep an eye on all suspected foreign fighters, since 10 to 12 security personnel are needed to monitor suspects continually.

Montasser AlDe’emeh, a social worker who counsels former foreign fighters in Molenbeek, expressed disbelief and shock at the Paris attacks. He told Belgian media on Sunday that after witnessing Friday’s attacks, he would stop counseling foreign fighters who return to Belgium. “We need to give them a sign that if they leave [for Syria], they're making a definite choice and can't return,” he told Het Nieuwsblad, a Belgian daily.