One of the Brussels bombers once worked as a cleaner at the European Parliament, officials say.
The man had month-long summer jobs there in 2009 and 2010, the EU Parliament said, without revealing his identity.
However, sources say he is Najim Laachraoui, one of the airport bombers.
Belgian PM Charles Michel has defended his country’s approach to fighting terror threats, insisting Belgium is not a “failed state”.
Charles Michel said everyone in authority had to take a share of the blame for failings before and after March 22.
Najim Laachraoui, already a major suspect on the run after the Paris attacks in November, was named as one of the two bombers who targeted Zaventem airport.
The EU Parliament said the cleaning company had provided proof that the person hired had no criminal record at the time.
PM Charles Michel said 30 measures were being put place in Belgium, including a ban on pre-paid mobile phone cards.
“Our key message today is we return to normal life in Brussels and in Belgium,” the Associated Press quoted him as telling reporters.
“When there is an attack like that of course that’s a failure and nobody can deny this,” he said.
“[But] I cannot accept the idea that we’re a failed state.”
Belgium has been accused of taking an un-co-ordinated approach to terror threats because it has multiple institutions representing the country’s complex linguistic and political makeup.
The Brussels region alone has six police zones.
According to Belgium’s De Tijd newspaper, Charles Michel said it was “short-sighted to say a unified police force could have prevented the attacks”.
He said there had been some successes like the recent arrest of the surviving suspect of the Paris attacks last November, Salah Abdeslam, adding it had taken 10 years to track down al-Qaeda leader Osama bin Laden after the 9/11 attacks in the US.
The search for the March 22 attackers is not yet over as pictures taken at Zaventem airport show three men entering the terminal building with explosives.
Najim Laachraoui and Ibrahim el-Bakraoui detonated their bombs and the third is thought to have escaped.