The taxi driver who drove the Brussels suicide bombers to the airport was not allowed to touch their explosives-laden bags and they sat in silence during the journey, Belgian newspaper DH reported citing unidentified sources.
Brahim El Bakraoui and two other men suspected of carrying out the attack on Tuesday travelled from the Brussels district of Schaerbeek to the airport.
The airport bombs and a suicide bombing at Maelbeek metro station in the city centre, which prosecutors said was carried out by El Bakraoui's brother Khalid, killed at least 31 people and injured 270.
A man wearing a hat and light-coloured jacket did chat with the taxi driver, talking about his anger towards the United States and how he disagreed with some of its actions, DH said.
A bespectacled man wearing a cream jacket and black hat ran out of the airport terminal, federal prosecutors said, before a third suitcase bomb exploded in the departures area as bomb disposal experts were clearing the area, causing no casualties.
The man, captured on film with the suicide bombers, is being sought by police.
DH said the taxi driver smelled ammonia during the journey and when he dropped the men off at the airport noticed their bags had traces of white powder on them.
He heard about the explosions while driving his next passenger and immediately went to the police, it said.
On Wednesday, DH reported that a mix-up by a Brussels taxi dispatcher meant a small car was sent to pick up the bombers instead of the minivan they had ordered and the passengers were forced to leave one bag behind. Police later found a nail bomb in an apartment in Schaerbeek.