BRUSSELS (AP) — More than four years after suicide bombings killed 32 people and injured hundreds in the Brussels subway and airport, massive pre-trial hearings started Monday on the outskirts of the Belgian capital to determine which suspects will eventually be tried.

The hearings — mainly procedural — are set to last 10 days and are the final step before a trial on terror charges can start next year.

Brussels has one of world’s biggest courthouse, but the decaying Poelaert Palace of Justice in the heart of the city has been deemed unfit to host the behind closed door hearings, mainly for security and sanitary reasons. Instead, judges, lawyers, suspects and 650 plaintiffs will gather over the next two weeks at the former NATO headquarters.

The high-security building has been refurbished for the occasion, equipped with hearing rooms and prison cells. The vast complex also offers enough space to guarantee social distancing during the COVID-19 pandemic. Renamed “Justitia," the complex will host the proper trial following further construction work estimated at €20 million ($24 million).

Around 900 people are among those who suffered physical or mental trauma in the March 22, 2016 attacks, which were claimed by the Islamic State group.

Earlier this year, the federal prosecutor’s office requested that eight of the 13 main suspects should be referred to the criminal court of assizes — the court that tries the most serious crimes — for charges of assassinations and attempted assassinations in a terrorist context, and for belonging to a terrorist group

Among them is Salah Abdeslam, the lone known surviving suspect in the 2015 deadly Paris attacks, and Mohamed Abrini, the Brussels native who walked away from Brussels' Zaventem airport after his explosives failed to detonate.

Abdeslam was captured in Brussels on March 18, 2016, and his arrest may have prompted other members of the Islamic State cell to rush attack plans already in motion. Four days later, suicide bombers detonated their explosives in the Brussels airport and metro during the morning rush hour.