The interview took place after Brahim Abdeslam returned from Turkey after a failed bid to get to Syria. Belgian prosecutors then believed that the brothers did not pose a threat.
Brahim Abdeslam is one of the terrorists who blew himself up in Paris. Salah is thought to have made it back to Brussels alive and is being tracked down.
Eric Van Der Sypt, spokesman for the Belgian federal prosecutors, says that Brahmin wasn’t prosecuted because no evidence that he took part in terrorist activity was found.
"We knew that both brothers had been radicalised and that they might go to Syria, but they didn't seem to form a direct threat."
As a result the French authorities were not alerted.
In the past Salah Abdeslam and the suspected brain of the Paris attacks Abdelhamid Abaaoud were prosecuted in connection with an armed attack.