Belgian authorities have charged four more suspects with “participating in terrorist acts” linked to the deadly suicide bombings in Brussels, the federal prosecution office said Saturday.

Belgium’s Federal Prosecution Office said in a statement Saturday that Mohamed Abrini, Osama K., Herve B. M. and Bilal E. M. were all charged with participating in “terrorist murders” and the “activities of a terrorist group” in relation to the March 22 bombings in Brussels’ airport and subway. The attacks killed 32 people and wounded 270 others.

Two other suspects arrested in the last couple of days have been released “after thorough interrogation,” the statement said.

The statement notes it was “not possible yet to confirm” if Abrini was the third suspect in the Brussels Airport bombing — dubbed “the man in the hat.”  That man escaped Brussels Airport while two suicide bombers he was seen with on video blew themselves up at the airport and another bomber attacked the city’s subway.

The charges follow days of arrests and raids in in Brussels and could give investigators new insights into the Islamic State group cell believed to have carried out both the attacks in Brussels and the Nov. 13 attacks in Paris, which left 130 dead in the French capital.

Brussels remains under terror alert

Osama K. was identified by Swedish media as Osama Krayem, who is known to have left the Swedish city of Malmo to fight in Syria. The prosecutor’s office suspects he may be the second person present at the attack on the Maelbeek subway station in Brussels and also may have been present at a shopping mall where the luggage used in the airport attack was purchased.

Swedish officials had no immediate comment on Osama K.

The statement describes Herve B. M. as a Rwandan national arrested at the same time as Krayem who is accused of offering assistance to both Abrini and Krayem.

The attacks in France and Belgium were the two biggest attacks carried out by the Islamic State group in Europe over the past year. The arrests may help investigators unravel the links between the attacks and IS, the radical Muslim group that controls territory in both Iraq and Syria.

Krayem had earlier been identified posting photos from Syria on social media, according to Magnus Ranstorp, a counterterrorism expert at the Swedish National Defence College.

“He also tried to recruit people in Malmo,” Ranstorp told The Associated Press.

The detentions were a rare success for Belgian authorities, who have been pilloried for mishandling leads in the bombings investigation. Evan after multiple arrests, Brussels remains under the second-highest terror alert, meaning an attack is still considered likely.