Abdelhamid Abaaoud is the key suspect behind the Paris attack. Right now he is believed to be in Syria with ISIS. The 27-year-old was raised in Molenbeek, a district of Brussels known for its many Arab immigrants, its high unemployment rate, and its overcrowded housing—perfect breeding grounds for terrorism.

He is an associate of Salah Abdeslam, who is on the run after the Paris massacre, and Salah’s brother, Brahim, who blew himself up during the attacks. Brahim died in the Comptoir Voltaire bar, without killing others, while other jihadis carried out deadly suicide attacks across Paris. They are all believed to have been recruited by Daash.

Abaaoud is closely connected with Mehdi Nemmouche, a jihadi of Algerian origin, who shot and killed four people at the Jewish Museum in Brussels in May, 2014. Nemmouche lived in the hotbed area of Molenbeek—an area where, Belgian officials admit, radical Islamist ideology is strong and popular with young Muslims. In recent years, Molenbeek has had “the highest concentration of foreign terrorist fighters in Europe,” said Liesbeth van der Heide, of Leiden University’s Centre for Terrorism and Counterterrorism in the Netherlands. Belgium has produced more people who have gone to fight for ISIS than any other EU country.

Salah Abdeslam.

“Belgian authorities suspect that Abaaoud helped organise and finance a terror cell in Verviers, Belgium. It was disrupted by police raids in January. Two jihadis were killed in Verviers—later identified by ISIS as Khalid Ben Larbi (alias Abu Zubayr, 23) and Soufiane Amghar (alias Abu Khalid, 26).”