Belgian prosecutors have launched a public appeal seeking any information on the "man in hat" suspect in the Brussels Airport suicide bombings that killed 16 people.
Belgian Federal Prosecutor Eric Van der Sypt said authorities were especially interested in any people who might have filmed or photographed the man.
He was seen at the airport with two suicide bombers before they died in the March 22 attacks. A subsequent explosion at Brussels' Maelbeek subway station killed another 16 people the same morning.
Photos released by prosecutors showed the "man in hat" leaving the airport on foot, walking to the nearby town of Zaventem and then into Brussels, where all traces of him were reportedly lost.
The suspect also wore a white jacket but discarded it at some point, prosecutors said.
The appeal for public assistance more than two weeks after the suicide bombings indicated that investigators have hit a standstill. Three bombers, two at the airport and one in the subway, also died in the attacks, which were claimed by Islamic State.
According to a video reconstitution of the suspect's itinerary presented to reporters, the man left the Brussels Airport terminal at 7.58am before two other men he was with in the building exploded suitcases laden with explosives. He passed by a Sheraton hotel, walked through the town of Zaventem, discarded his jacket, and was seen on video footage at Meiser square in north-eastern Brussels at 9.42am.
Eight minutes later, his trail vanishes.
Belgian authorities are hoping that they or someone finds the discarded light-coloured jacket, saying it could yield precious clues. Federal prosecutor Thierry Werts also said there had been many people around the hotel when the suspect walked by who may now be overseas, and asked for their assistance as well.
Prosecutors asked "people who might have filmed or taken a photograph of the suspect or think they can provide extra information" to call a special telephone number or to email authorities.