Belgian prosecutors have released new footage of the key surviving Brussels airport attacks suspect, showing the route he took after leaving the area.
They have asked members of the public who saw the man to come forward.
The man was tracked on CCTV footage until 09:50 local time and was wearing a hat and a light-coloured jacket, officials said.
His trail was lost close to the EU institutions in Brussels' city centre, not far from Maelbeek metro station.
Prosecutors said he had discarded the jacket, and have asked the public to report if it has been found.
The 22 March attacks by so-called Islamic State (IS) on Brussels airport and the Maelbeek metro station killed 32 people.
Three attackers are believed to have targeted the airport, with two dying in the bomb blasts. Another died in the metro attack.
The "man with the hat", as prosecutors called him, was captured pushing a trolley at Brussels airport next to the two suicide bombers in previously released CCTV footage.
The new footage shows the suspect briefly running amongst passengers as they try to escape the scene at the airport, before walking some 10km over a two-hour period.
He was last seen about 40 minutes after the Maelbeek metro bombing.
The suspect's route caught on CCTV
After 07:58: Leaving the airport
The suspect is seen leaving the airport after the explosions. He is wearing a light-coloured jacket, pale blue shirt and a distinctive hat.
He passes in front of the Sheraton hotel and leaves the airport near the Avis vehicle rental car park.
08:50: Junction of Grote Daalstraat and Chaussee de Louvain
At some point after leaving the airport, the suspect gets rid of his jacket. He is next captured on CCTV at 08:50 at the junction of Grote Daalstraat and Chaussee de Louvain, heading towards the city centre. His shirt sleeves are rolled up.
09:42: Meiser junction
The man takes the Chaussee de Louvain and is next seen on camera at the Meiser junction.
09:50: Chaussee de Louvain to Avenue de la Brabanconne
The suspect continues along the Chaussee de Louvain and then takes the Avenue de la Brabanconne, where he disappears at the junction with Rue du Noyer at 09:50. He is last seen wearing a light blue shirt with dark elbow patches and the hat.
Federal prosecutor Eric Van Der Sypt asked for those who "might have filmed or taken a photograph of the suspect" or believe they have any useful information, to call 0800 30 300 (in Belgium) or 00 32 25544488 (from abroad).
'Delayed extradition'
Separately Salah Abdeslam, the main suspect in the Paris terror attacks of 13 November, will not be extradited from Belgium to France for several more weeks, his lawyer Sven Mary has said.
Belgian authorities want more time to question Abdeslam in connection with a 15 March shootout in Brussels during a police raid, he said.
According to prosecutors, Abdeslam's fingerprints were found in the apartment where Algerian terror suspect Mohamed Belkaid was shot dead after opening fire on police.
Abdeslam was arrested three days later in Brussels' Molenbeek neighbourhood.
He is believed to be the only surviving member of the group that killed 130 people in Paris last November in a series of co-ordinated attacks also claimed by so-called IS.
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