A man known as Faycal C, the only person arrested and charged with involvement in the Brussels attacks, has been released for lack of evidence.
A BBC report has said, the Belgian media have given the man's full name as Faycal Cheffou.
Police have released CCTV footage in their efforts to identify a third suspect in last Tuesday's bomb attacks on a Brussels airport.
Attacks on the airport and the city's metro system killed 35 people and injured more than 300.
The attacks were claimed by the so-called Islamic State militant group.