Belgian Federal Police are hunting for this man as suspect Faycal Cheffou was released from custody.

Belgium authorities believed they had caught the mystery man seen in security footage with the two suicide bombers at Brussels airport when Fayçal Cheffou was charged on Saturday.

But the search for the unknown man continues after Mr Cheffou was released from custody due to a lack of evidence.

It has raised fresh questions about the handling of the case by under-fire Belgium authorities.

Belgium authorities have now released CCTV footage of the only surviving suspect who is believed to be still at large.

Police released fresh video of a man in a hat and white jacket pushing a trolley with a large bag through the departure hall, next to suicide bombers Ibrahim El Bakraoui and Najim Laachraoui.

The 30-second video shows the mystery man in his infamous white coat, glasses and black bucket hat walking alongside the two suicide bombers.

It appears the man smiles and communicates with his alleged accomplices. Previously, authorities had only released CCTV images of the suspects.

A close up of ‘the man in the hat’.

‘The man in the hat’ is believed to be still at large.Source:Supplied

Faycal Cheffou speaking in a video posted on YouTube in 2014 in which he calls himself an independent journalist demanding the authorities respect the rights of asylum-seekers.Source:AFP

MAN CHARGED THEN RELEASED

Prosecutors had charged a man, identified by local media as Fayçal Cheffou, on Saturday with participation in a terrorist group, terrorist killings and attempted terrorist killings in relation to the March 22 Zaventem airport attack.

They were investigating whether he was the third unknown attacker who fled after his bomb did not go off after he was arrested on Thursday evening.

But Mr Cheffou is a now free man, with authorities claiming there was a lack of evidence.

“The indications that led to the arrest of Faycal C were not substantiated by the ongoing inquiry,” read a statement from the Belgium federal prosecutor’s office.

“As a result, the subject has been released by the examining magistrate.”

Mr Cheffou, an independent journalist, was widely reported as the third attacker after authorities released the CCTV images. It was believed he had links to radical Islam.

In 2014, Mr Cheffou produced a documentary outlining the mistreatment of Muslim prisoners in a Belgium jail. YouTube footage of the documentary shows Mr Cheffou walking out the front of the prison as prisoners yell toward the camera in the background.

In a piece to camera, Mr Cheffou blames politicians and the media for being “disrespectful of human rights”.

‘RIDDLED WITH BUNGLES’

His release comes as a new blow to an inquiry dogged by accusations that Belgium missed a series of leads in cracking down on a jihadist network linked to the Brussels bombings as well as the November Paris attacks that killed 130 people.

“This anti-terrorism effort in Belgium has been riddled with bungles for the last few months and this is just another embarrassing backdown for them,” Channel 9’s European correspondent Tom Steinfort told 3AW Breakfast.

“[These are] serious charges — terrorist murder — and now they’ve come out and said, ‘We actually don’t have sufficient evidence to proceed’. They’ve now got to the point where they all of a sudden had a powwow back at the office and said, ‘Well hang on, no, we don’t actually have the evidence we need to get a prosecution here, we might have to put this on ice’.”

Belgian officials said Monday that the death toll had climbed to 35 after four people died in hospital.

The attack included twin blasts at the airport and a further suicide bomber at Maelbeek Metro station.

Brussels is still trying to get back on its feet, with the airport saying it would carry out a test run Tuesday to see if repair work in the wrecked departure hall was satisfactory, but it could not give a firm date for resuming services.

Belgian authorities are continuing to face criticism over whether they could have prevented the tragedy, as the links to the Paris attacks become clearer by the day.

Ibrahim’s brother Khalid El Bakraoui, who blew himself up on a Brussels Metro train shortly after the airport blasts, is meanwhile believed to have rented a property linked to Paris prime suspect Salah Abdeslam.

Abdeslam was arrested in Brussels on March 18 just metres from his family home after four months on the run.

Turkey accused Belgium last week of ignoring a clear and present danger after revealing it had deported Ibrahim El Bakraoui as a “terrorist fighter” last year after arresting him near the Syrian border.

Two Belgian ministers offered to resign after the Turkish link emerged. Prosecutors earlier said three men arrested in raids in Belgium at the weekend had been charged with “participation in the activities of a terrorist group” but that no direct link had been established with the Brussels attacks.

The dead from the March 22 attacks include four Americans as well as people from China, UK, Sweden and Peru — testament to the cosmopolitan nature of a city that is home to both the European Union and NATO.

Ninety-six people remain in hospital.

— youngma@news.com.au