Belgian authorities face growing criticism for a series of mistakes and missed chances in connection with a jihadist cell linked to both the Brussels and Paris attacks.
Following the release on Monday of the only man charged over the Brussels airport and metro attacks, here are some of the key errors:
In one of the most embarrassing mix-ups to date, Belgium on Monday released a man identified as Faycal C, two days after he had been charged with offences including "terrorist murder".
Prosecutors had said they were working on the theory that he could be the third bomber at the airport whose device failed to go off, and who has been dubbed the "man in the hat" on account of the outfit he was seen wearing in security footage.
Immigration Minister Theo Francken called him a "jihadi creep" in a tweet on Monday morning, but hours later prosecutors said they were releasing him because of a lack of evidence.
Key Paris attacks suspect Salah Abdeslam was questioned for only three hours between his arrest in Brussels on March 18 and the attacks on March 22, raising questions about whether authorities could have done more to extract information from him about his accomplices.
Prosecutors said he was asked only about Paris, after which he exercised his right to silence.
In a damning revelation, Turkish President Recep Tayyip Erdogan said Belgium had ignored warnings from Ankara following the arrest of Ibrahim El Bakraoui near the Syrian border in June 2015. Bakraoui was one of the bombers at Brussels airport.
Belgium's police liaison officer in Istanbul was informed he had been arrested but failed to try to get more information about him or his record.
Bakraoui was then deported to the Netherlands at his own request, but Turkey only warned the Belgian and Dutch ambassadors at the last minute, too late for authorities to catch him on arrival.
Belgian Interior Minister Jan Jambon and Justice Minister Koen Geens both offered to resign over the matter but Prime Minister Charles Michel asked them to stay on.
Bakraoui and his brother Khalid, who blew himself up at Maalbeek metro station, both had records of violent crime. Ibrahim served four years in jail after a gunfight with police while Khalid served jail time for carjacking.
After the attacks, prosecutors said that while the two had an extensive criminal record they had no apparent links to terrorism.
In reality, Khalid Bakraoui was the subject of an international arrest warrant over the Paris attacks, and both brothers were on US terror watch lists.
The morning after the Paris attacks, Abdeslam was able to drive back to Brussels despite being stopped at three police checkpoints in France. Several people were later charged with helping him.
At one point, he was reported to have escaped from a house while hidden in a piece of furniture. On another occasion, police were forced to postpone a raid because of a Belgian law banning searches at nighttime.
It later emerged that European authorities failed to notify each other when Abdeslam travelled back and forth across Europe alongside several people involved in the cell in the months before the Paris attacks, despite suspicions about him and his brother Brahim, who blew himself up in a bar in the French capital.
Abdeslam was finally caught on March 18 -- about a block away from his family home. Traces of his DNA and fingerprints have been found in several other locations around Brussels.
Belgian authorities have also come under fire for failing to track jihadists returning from fighting in Syria and Iraq with the Islamic State (IS) group, which claimed both the Paris and Brussels attacks.
Abdelhamid Abaaoud -- the ringleader of the Paris attacks who was also in contact with a jihadist cell that was broken up in the Belgian town of Verviers in January 2015 -- featured in IS propaganda talking about his time in Syria and bragging about how he had evaded European security forces.
In April 2015, the school in Brussels attended by Bilal Hadfi, another of the Paris bombers, reportedly raised concerns about his radical views and informed education authorities that he had gone to Syria, but the information was not passed on to police.
Paris bomb-maker Najim Laachraoui, who blew himself up at Brussels airport, had also travelled to Syria. Belgian police issued a wanted notice for Laachraoui the day before the Brussels attacks.
The Abdeslam brothers were reportedly questioned by Belgian police after Brahim tried to travel to Syria in 2015, a few months before the Paris attacks, but only got as far as Turkey.
However, the pair were released without charge. The Belgian authorities also failed to notify the French authorities, as the two brothers are French nationals.
Belgian authorities have long been accused of failing to tackle radicalisation, especially in the gritty, largely North African immigrant district of Molenbeek in Brussels. Many of the Brussels-Paris cell knew each other growing up in the neighbourhood but these links were never fully followed up.
Belgian authorities are fighting among themselves about whether they should have stopped the metro system after the airport attacks.
The interior minister says he decided to order a halt at 8:50 am, 20 minutes before the metro bombing, but the operator says it never received such an order.