Officials believe they've identified the third man seen on a security camera just before the bombing of the Brussels airport.
The suspect's name was not released, but authorities said he was listed on U.S. terrorism databases before the bombings. He is believed to be on the run.
Belgian law enforcement confirmed that suspected suicide bombers Khalid and Ibrahim El Bakraoui were killed in the attacks.
A suspected bomb-maker from the November attacks in Paris, Najim Laachraoui, is also believed to be a suicide bomber involved in the Brussels airport attack.
Investigations into the attacks have led to six people in Brussels being detained in police raids.
Police were tight-lipped about the arrests but said they would decide Friday whether those apprehended would remain in police custody.