Belgian prosecutors have launched a fresh appeal for help in finding the suspected third attacker in last month’s bombings at Brussels airport, releasing new video footage and pictures of the so-called “man in the hat”.

Police have been desperately searching for the man ever since he was filmed next to the two suicide bombers who blew themselves up at Brussels airport on March 22, in co-ordinated attacks that also struck a metro station in the city — a total of 32 people died.

“We especially appeal to anyone who might have filmed or think they have photographed the suspect,” spokesman Eric Van der Sypt said at a press conference in Brussels.

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The newly released police video shows the suspect, wearing a hat and a light-coloured jacket, fleeing the airport’s departure hall after the bombs went off at 7:58am (local time).

CCTV footage shows him continuing his route on foot towards central Brussels, where surveillance images lose sight of him at 9:50am.

Khalid (left) and Ibrahim El Bakraoui also carried out attacks. Photo: Supplied

Along the way, the man discards his jacket and at one point appears to be on the phone.

Investigators are still looking for the jacket, described in a statement as “bright with a hood which is dark inside”.

“It is especially the coat which interests us,” Mr Sypt said, asking if anyone might have seen it along the suspect’s route.

Potential witnesses were asked to contact the police using a specially provided phone number and email address.

Last week police asked all residents and business owners in the Brussels region who have external surveillance cameras not to delete any footage from March 15 onwards.

Belgian authorities have been criticised for not doing enough to tackle the rise in homegrown extremism, as close links have emerged between the Brussels attackers and those behind the Paris terror assaults in November which left 130 dead.

Both attacks were claimed by the Islamic State (IS) group.