Chakib Akrouh, a suspected gunman in the Paris attacks whose identity was released in Paris yesterday, used a one-way ticket to fly from Brussels to Istanbul on January 4, 2013, the federal prosecutor's office said.
"The investigation then indicated his presence in Syria from January 2013 when he joined the ranks of the Katibat al-Muhajereen, then the Islamic State of Iraq and the Levant," it said in a statement, using another name for the Islamic State.
Akrouh had been holed up in an apartment in the northern Paris suburb of Saint-Denis with the suspected ringleader of the Paris attacks, Abelhamid Abaaoud, who was also a Belgian of Moroccan origin.
Akrooh blew himself up when police raided the flat, while Abaaoud and a French woman, Hasna Aitboulahcen, who is thought to have been Abaaoud's cousin, were also killed.
Prosecutors initially mistakenly said the woman had been the suicide bomber.
The Belgian prosecutor said a court in Belgium sentenced Akrouh to five years in jail in absentia last July over jihadist recruitment network sending fighters to Syria.
The Belgian prosecutor's office said "an analysis of photographs from the person seen at the side of Abdelhamid Abaaoud in the Paris metro on November 13, 2015 at 10:14 PM after the Paris attacks, allowed federal investigators to make the link on December 17 2015 with with the so-named Chakib Akrouh."
It added that "a DNA test from (Akrouh's) mother was carried out on December 17, 2015 and the comparison with the DNA sample from the blast site in Saint Denis confirmed it was that of Chakib Akrouh.