Abrini's arrest yesterday, along with five other suspects, marks an important step in the investigations into the November 13 Paris attacks, which killed 130, and the March 22 assault on Brussels which left 32 dead.
In both, several of the suspects came from the largely-immigrant Molenbeek neighbourhood of Brussels, including Abdelhamid Abaaoud, said to have played a key role in Paris, along with Salah Abdeslam who was arrested on March 18.
The Belgian authorities have faced intense criticism over their handling of the attacks as it emerged many of the suspects were known to police for a long time.
Critics say the government has not done enough to prevent radicalisation of Muslim youth in areas such as Molenbeek, with Belgium proportionately the biggest source in the European Union of foreign fighters going to join IS in Syria.
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There has been intense speculation Abrini is the third, hat-wearing suspect seen alongside two suicide bombers in security footage at Brussels airport.
Belgian police on Thursday released a video showing a man wearing a hat and light-coloured jacket who was seen with the two suicide bombers in the departure hall.
While they blew themselves up, he fled and made his way on foot back to central Brussels, appearing calm and composed before disappearing.
Today, La Libre daily carried a cartoon showing a policeman kicking a man holding a hat into a prison cell under the banner: "They criticise the Belgian police but ... Hats off!"
Ibrahim's brother Khalid blew himself up at Maalbeek metro station not far from the European Union quarter in Brussels.
Abrini was arrested in the Brussels neighbourhood of Anderlecht, the prosecutor's spokesman said yesterday. Two others were also picked up with him but there were no immediate details on their identities.