Belgian and French prosecutors met in Brussels to discuss the probe into the November carnage following Friday's dramatic arrest of prime suspect Salah Abdeslam in the Belgian capital after four months on the run.
Belgian investigators named a suspected accomplice in the deadly November 13 attacks as Najim Laachraoui, who was previously known by the false name of Soufiane Kayal.
Laachraoui used the false name to travel to Hungary in September with Abdeslam, who is the last known survivor of the 10 Paris attackers. Laachraoui is also believed to have travelled to Syria in February 2013.
"We have not a bad amount of pieces of the puzzle and in the last few days several pieces have found their place," Frederic Van Leeuw told a news conference in Brussels, flanked by Paris prosecutor Francois Molins.
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"But... We are still, far from solving the puzzle."
Van Leeuw also admitted they "don't have the full timeline" for what Abdeslam did between November 14, when he evaded three French police checks and escaped to Brussels, and his arrest.
Belgian authorities have been embarrassed by the revelation that Abdeslam was found just around the corner from his family home in the gritty Brussels neighbourhood of Molenbeek, and may have been aided by friends and family.
Molins, the French prosecutor, meanwhile said that France expected Abdeslam to be extradited to face trial over the attacks, despite his lawyer saying that he would fight the process.
"There is a strong expectation from the French justice authorities and particularly from the families of the victims that Salah Abdeslam comes to explain himself," Molins said.
"The president, in light of recent events, will update them on what is happening," the presidential palace said.
Molins said at the weekend that Abdeslam played a "central role" in the attacks and originally planned to "blow himself up" at the Stade de France stadium but changed his mind.