Interpol and Europe's Schengen Information System knew about brothers Salah and Brahim Abdeslam, related to the French attack on 13 November.
Brahim and Salah both meant to blow themselves up during the Paris attacks on 13 November. While Brahim followed through, Salah did not and is on the run.
An international arrest warrant has been issued for Salah Abdeslam.
The brothers featured on a list of 837 Belgian residents who had links to radical Islam, according to information received by the newspaper group Sudpresse from the Interior Ministry of Belgium.
The list had been shared with the international police cooperation body Interpol, and EU's inter-governmental security database, Schengen Information System, on 29 October, the newspaper said. It added: "This did not stop Salah Abdeslam from travelling freely on the morning of the attacks."
The morning after the attacks, he was stopped at a French town, Cambrai, where after a routine identity check he was permitted to continue travelling to Belgium, where he was returning after his failed attempt at bombing in Paris.
The Belgian Police, which have been conducting raids in Brussels and around, have eight suspects in custody, IANS quoted Belgian broadcaster RTL as saying.
Those in custody are Hamza Attouh, Mohamed Amri, Lazez Abraimi and Ali Oulkadi, who are suspected of providing help to Salah for getting back to Belgium.
Abdeilah Chouaa and Mohamed Bakkali were arrested on 23 and 26 November after raids, but the reason behind their detention has not been disclosed by the Belgian federal prosecutor.
Samir Z and Pierre N are also in custody for their links to Bilal Hadfi, the first suicide bomber who blew himself up that fateful night at the Stade de France.
One individual walking nearby had been killed while several others were injured. The damage was limited as the bomb was of poor quality, the Paris prosecutor Francois Molins said, according to a CNN report.