Belgian authorities have issued a new appeal for information about a man caught on CCTV at Brussels airport with two others who are thought to have blown themselves up in the check-in area last Tuesday.
Belgian Federal Police released on Monday a 32-second video of a mysterious man in a hat seen in the company of the airport suicide bombers, indicating that he could still be at large.
Earlier this week, Belgian media had claimed a detained man named Faycal Cheffou, was the mysterious suspect in the white jacket and dark hat.
Police at the time would not comment on those reports, but charged Cheffou on Saturday with "taking part in a terrorist group, terrorist murder and attempted terrorist murder".
But Cheffou was freed on Monday following a lack of evidence linking him to the carnage, Belgian prosecutors said. 
"The clues that had led to the arrest of [the person] named Faycal C were not backed up by the progression of the ongoing investigation," the federal prosecution said in a statement.
Authorities also announced that the number of victims from last week's airport and subway suicide bombings rose to 35.
On Monday, Belgian Health Minister Maggie De Block announced on her Twitter account that four of those hospitalised after the bombings had died of their injuries.
She posted: "Four patients deceased in hospital. Medical teams did all possible. Total victims: 35. Courage to all the families."
De Block reported over the weekend that 101 of those wounded in the blasts were still being treated in hospitals, including 32 in burn units. 
On Sunday, investigators launched raids in Brussels and two other cities, taking four more people into custody.
The Belgian Federal Prosecutors Office provided no details of the alleged actions committed by the suspects and said the fourth person detained on Sunday was released without charge.
bombings, the bloodiest tragedy in recent Belgian history, were claimed by the Islamic State of Iraq and the Levant (ISIL).
Several people have been arrested on terrorism charges in Belgium, France, Germany and Italy since the attacks in Brussels.