That's what investigators are trying to determine after nabbing Mohamed Abrini in a police operation in the Anderlecht district of Brussels. Abrini has been tied to the terror attacks on Paris last November through surveillance video and DNA. Authorities now can question him about the Brussels airport bombing on March 22, part of the attacks that killed 32 people.
Two bombers died at the airport. A third man wearing a hat is seen on video walking with them. Authorities said he fled.
Investigators also are trying to determine whether a man arrested in a separate operation Friday was part of the second attack -- at a Brussels metro station -- an hour later. Osama Krayem -- also known as Naim al Hamed
-- might be the second person "present at the time of the attack at the Maelbeek subway station," Belgian federal prosecutor's spokesman Eric Van der Sypt said.
Authorities have said Khalid El Bakraoui carried out the metro attack and Van der Sypt said that another person was seen with El Bakraoui before the subway blast.
Van der Sypt said surveillance video from a mall shows the second person buying the bags used in the airport attack.
Abrini, a 31-year-old Belgian-Moroccan, had been among Europe's most wanted and was considered "armed and dangerous."
His arrest means that Belgian authorities now have at least two people, along with Salah Abdeslam
, who have been directly tied to the attacks in Paris.
Abrini was seen with Abdeslam at a gas station between Brussels and Paris two nights before the Paris massacre. His DNA and fingerprints were lifted from a vehicle used in the Paris attacks, spokesmen for the Belgian federal prosecutor said.
"For French investigators, this can be very big," said CNN's Nic Robertson. "This gives you a much stronger position to be in to get to the truth ... to (track) other terrorists on the run down," Robertson said. "And also to understand precisely what happened in Paris."
But according to Peter Bergen, a leading terrorism expert and CNN analyst, Abrini's arrest puts pressure on Belgian authorities to find out information quickly.
Days after Abdeslam was arrested, terrorists carried out twin attacks in Brussels. A senior counterterrorism official has said the 26-year-old was probably going to be part of an attack planned by the same ISIS cell.
"Hopefully, Belgian counterterrorism officials won't make the same mistake they made last time with Abdeslam," said Bergen, vice president of the New America public policy institute. "They didn't ask him about what else was in the pipeline."
Who is Mohamed Abrini?
According to a European police cooperative known as ENFAST
, video showed Abrini with Abdeslam on November 11, two days before the massacre in the French capital.
The same Renault Clio that Abrini drove was used in those attacks, ENFAST reports. Abdeslam told authorities he drove a car of that same make and model to the Stade de France -- where suicide bombers detonated explosives outside a soccer game -- and abandoned it.
He then wandered into the subway and allegedly "contacted one person," that being Abrini
, CNN's French affiliate BFMTV reported.
Abrini has a criminal record of violent theft. He also had
a younger brother killed while fighting for ISIS in 2014, and he was in Istanbul, Turkey, briefly last summer and possibly in Syria.
Relatives have insisted Abrini was in Brussels the night of the Paris attacks.
More than four months later, Belgian state broadcaster VRT reports Abrini was still in the Belgian capital -- playing a hands-on role in the terror attacks there.
He is "more than likely" one of three men shown on surveillance video rolling luggage carts through Brussels airport, according to VRT.
On Thursday, Belgian police released a series of surveillance images showing the third man leaving the airport in Zaventem, then heading west into the Brussels district of Schaerbeek, over the course of two hours following the bombings.
Last month, two friends told CNN
that Abrini was a regular customer at a cafe in Brussels called Les Beguines. They said he used to visit in the evenings for a drink, and described him as a tall, slim, quiet man who would keep to himself.
Who is Osama Krayem?
The other identified person arrested, Krayem, has been described as "very dangerous and probably armed" in a bulletin circulated by French investigators to European security services hours after the Brussels attacks.
A French source close to the investigation into ISIS' terror network in France and Belgium told CNN that European security agencies believe Hamed, or Krayem, had an operational role in the Brussels attack.
Krayem was a resident of Malmo, Sweden, and was known to Swedish counterterrorism services and suspected to have joined ISIS in Syria, Magnus Ranstorp, a Swedish counterterrorism expert at the Swedish National Defense College, told CNN.
Krayem posted images of himself from Syria with automatic weapons and the ISIS flag, Ranstorp said. The final post he made on Facebook from Syria was in January 2015, Ranstorp said.
The French newspaper Le Monde reported last month that the 28-year-old's DNA was found at the apartment in Brussels' Schaerbeek district where the three airport attackers left from the morning of March 22.
Born on New Year's Day 1988 in Hama, Syria, he -- like at least two of the Paris attackers -- is thought to have come to Europe, along with hundreds of refugees from war-torn nations, via the Greek island of Leros.
Police operations ongoing
Abrini was arrested with two others in the Anderlecht operation, Belgian federal prosecutor's spokesman Thierry Werts told reporters.
Krayem and another person were taken into custody Friday in another police operation, this one in Brussels.
And the prosecutor's office revealed Saturday that a sixth person -- identified as Bilal Al Makhoukhi -- had also been arrested Friday, though it wasn't clear exactly where.
Officials said there were ongoing police operations into the night. The street where Abrini was arrested was cordoned off early Saturday. Forensic teams were still at work, according to a CNN crew at the scene. CNN's Frederik Pleitgen reported that authorities had removed bags of evidence from a residence.