Belgian prosecutors on Thursday appealed to the public for new information about the third attacker at the Brussels airport in the wake of suicide bombings last month that killed 32 victims.
On March 22, two attackers triggered bombs at the Belgian capital's international airport. A third set off an explosive in the Maelbeek metro station, near the Brussels headquarters of the European Union's main institutions.
The suspect who fled the airport - who has become known as the "man with the hat" based on surveillance images of him - had left another bomb that went off later, causing further damage but injuring nobody. He has been on the run since.
Investigators have now reconstructed his movements from the airport based on surveillance footage.
One recording shows him walking, then running, near the airport. He was then tracked heading on foot through the nearby town of Zaventem and into Brussels, towards the area where several EU institutions are based.
The airport explosions took place just before 8 am (0700 GMT), while the metro blast occurred around 9:15 am.
The suspect was filmed at 9:49 am on Chaussee de Louvain, a large street within the inner ring road of Brussels, before he disappeared a minute later on Avenue Brabanconne, which leads towards the EU institutions and the Maelbeek station area.
"We especially appeal to people who might have filmed or taken a photograph of the suspect," said federal prosecution spokesman Eric Van Der Sypt, adding: "All information will be handled discreetly."
Investigators are particularly interested in finding the jacket the man had been wearing in the airport, which he cast off as he walked through Zaventem. It is white, with a hood lined in a dark material.
A video released by police shows close-ups of the jacket and other clothing the suspect wore that day. Anyone with further information is asked to call a special hotline number.
The Brussels attacks took place four days after Belgian police arrested Salah Abdeslam, a suspect who had planned to take part in the November terrorist attacks in Paris that left 130 dead, but then backed out.
Belgian authorities extended his detention by a month Thursday, along with that of another suspect who was arrested with him - a man who has used the aliases Ahmed A and Amine Choukri, but whose real identity is not known.
The Belgian authorities agreed last week to a French request for Abdeslam's extradition. This will take place in the coming weeks, his lawyer Sven Mary said Thursday, according to the Belga news agency.
Abdeslam is to be heard in relation to a March 15 raid in the Brussels neighbourhood of Forest during which police were fired at, Mary said. One suspect died and four officers were injured after police tried to search an apartment linked to the Paris attacks.
Abdeslam will not be charged or interrogated in relation to the Brussels attacks, his lawyer said according to Belga.
The Brussels pretrial court also extended by a month the detentions of three other Belgians - Mohammed A, Mohamed B and Zakaria J - suspected of having links to the Paris attackers.
A fourth Belgian suspect, Abdellah C, was granted a conditional release, but remained in custody pending a decision by prosecutors on whether they would like to appeal.
Abdeslam allegedly attempted to contact this suspect after the Paris attacks, hoping that he could help fashion him a new identity, the Belga news agency wrote.
The court also took up the cases Thursday of several other men being held on terrorist charges related to different investigations.
This included two Algerian men, listed as Rabah M and Abderrahmane A, and linked to Reda Kriket, who was arrested in France on allegations that he was in the advanced stages of planning a terrorist attack in Paris. Their detentions were extended by one month.
The Belgian authorities also prolonged by one month the detention of three Belgian nationals, named as Mohamed B, Yassine A, and Aboubaker O, who have been charged with participation in the activities of a terrorist group.