A suspect told a Spanish court Tuesday that he had rented the vans used in in last week's attacks in Barcelona and Cambrils but thought they were going to be used for a house move, a person who attended the hearing said. Andreu will decide whether the four should be jailed or released.
Aalla is the alleged owner of the vehicle used to hit civilians and a police officer in Cambrils, a town that lies south of Barcelona.
Police said they had "scientific evidence" that Abouyaaqoub drove the van that barrelled through Barcelona's crowded Las Ramblas promenade, mowing people down, then hijacked a auto and fatally stabbed its driver while making his getaway.
Chemlal, arrested after an explosion at a bomb factory south of Barcelona, was covered in bandages and appeared to be wearing hospital pyjamas to today's court appearance, the Daily Mail reports.
The group is said to have stored more than 100 gas tanks and explosive ingredients at the house.
Chemlal was injured in an accidental explosion at the group's makeshift bomb factory on Wednesday evening.
The hearing was likely to end in the suspects being remanded in custody while the judge conducts an investigation that could take months or even years before a trial is organised.
The lone fugitive from the cell - 22-year-old Younes Abouyaaqoub - was shot to death Monday after he flashed what turned out to be a fake suicide belt at two police who confronted him in a vineyard not far from the city he terrorized.
The French daily Le Parisien reported on Monday that the vehicle came through the Paris region about a week before Thursday and Friday's attacks in Barcelona and Cambrils that killed 15 people.
Islamic State in Iraq and Syria (ISIS) claimed responsibility for the latest attack and a separate deadly assault, hours later, in the coastal resort of Cambrils, south of Barcelona.
Most of the 12 suspects lived in the town of Ripoll, set in forested hills beneath the Pyrenees north of Barcelona near the French border, and most were young men of Moroccan descent.
They were to testify before National Court Judge Fernando Andreu in Madrid.
Among those in court on Tuesday was Driss Oukabir, whose passport was found in the abandoned van after the Barcelona attack.
The four were interrogated in the presence of lawyers provided for them by the court.
Suspect Driss Oukabir was arrested Thursday in the northeastern town of Ripoll, as were two others identified by Spanish media as Mohammed Aalla and Salh el Karib.
No charges against the men have yet been specified. He is the lone survivor of a blast that destroyed a house in Alcanar, where police believe the cell was preparing explosives.
While Catalan police say the cell has been dismantled, investigators are trying to determine if it had logistical or other forms of support from other individuals.
One of his brothers, Said, was killed in Cambrils and a second, Youssef, is believed by police to have died in an explosion at a house used by the plotters at Alcanar, southwest of Barcelona, the day before the Barcelona attack.