Brussels (AFP) - Long before blowing themselves up in crowds of innocent people, suicide bomber Ibrahim El Bakraoui and his brother Khalid lived the lives of the classic Brussels hoodlum.

Carjackings, robberies and shoot-outs with police were just some of the convictions collected by the Belgian brothers who took part in the metro and airport assaults in Brussels claimed by the Islamic State group.

Both were said to have links with top Paris attacks suspect Salah Abdeslam, while the third identified Brussels attacker, Najim Laachraoui, was the suspected bomb-maker for the November rampage in the French capital.

Baby-faced Ibrahim, 29, who blew himself up at the airport on Tuesday along with Laachraoui, had been given a nine-year sentence in 2010 after a gunfight with police, according to local media.

He took part in a bungled robbery at a Western Union office in which a police officer was injured in the leg.

Turkey said it had detained Ibrahim in June last year as a "foreign terrorist fighter" and then deported him to the Netherlands.

President Recept Tayyip Erdogan said the Belgian authorities had failed to confirm his links to terrorism "despite our warnings" and had later released him, although it is not immediately clear when he crossed to Belgium from the Netherlands.

Ibrahim, seen on CCTV footage with two other suspects pushing airport trolleys with their bomb-laden bags, left a confused and scared message on an abandoned computer, according to the Belgian federal prosecutor.

"Hunted everywhere... no longer safe," Ibrahim said in the message. "I don't know what to do."

- Carjacker to suicide bomber -

His younger brother Khalid, 27, who blew himself at the Maalbeek metro station just a short walk from the main EU institutions, was a convicted carjacker, receiving a five-year sentence 2011, according to La Derniere Heure.

Federal prosecutors revealed Wednesday that both were Belgian citizens with convictions "not linked to terrorism".

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They burst into the public eye on March 15 when police raided an apartment in the Forest district of Brussels, as part of the investigation into the Paris attacks that killed 130 people.

Media reports said a joint squad of Belgian and French police approached the property because it was rented under a false name used by Khalid to secure a hideout months earlier for the Paris team.

Belgium filed an Interpol search for Khalid, who was suspected of renting other properties used to prepare the Paris attacks, including one in the southern Belgian city of Charleroi from where ringleader Abdelhamid Abaaoud set off to spearhead the assault.

The police last week fully expected to find an abandoned property, as utilities in the Brussels apartment had been shut off for weeks.

Instead they came under heavy gunfire, with one assailant killed and two men fleeing -- including, it is thought, Salah Abdeslam, then Europe's most wanted man who would be arrested three days later.

The brothers were not believed to have been present but their connection to Islamic State jihadism was established.

- 'Typical' student -

The second airport bomber was named as Najim Laachraoui, 24, who was captured on the CCTV footage with Ibrahim and another assailant who is the subject of a massive manhunt after his bomb did not go off and he fled the scene.

Investigators have found traces of Laachraoui's DNA on explosives used in the Paris gun and suicide bomb assaults, including at the Bataclan rock venue where 90 people died.

DNA traces were also found in a rural Belgian hideout used on the eve of the Paris attacks, as well as in a suspected bomb factory in the Schaarbeek district of Brussels.

Moroccan-born Laachraoui grew up in Schaarbeek and had been wanted by police over the Paris attacks since December, though by a false identity that was only unmasked last week.

Laachraoui attended Schaarbeek's Sainte-Famille Catholic school for six years where an official told AFP he was a "typical" student.

He received his baccalaureat, the equivalent of a high-school diploma, in 2009.

A newsletter posted on the school website indicated he studied electronics, but the official would not confirm this.

Laachraoui went to Syria in September 2013 in one of the first waves of jihadists to leave Belgium for the war-torn country, where he fought under the Islamic State nom de guerre Abu Idriss, according to media reports.

In February, a Belgian court convicted him in absentia for his involvement with IS.

He was known to have returned to Europe in September when he was checked by police under a false identity in a Mercedes driven by Abdeslam, who now sits behind bars in Belgium.

Also in the car was the Algerian Mohamed Belkaid, 35, shot dead during the March 15 search and gun battle in Brussels that eventually led to Abdeslam's capture.