MADRID -- A Spanish judicial official says two of the four surviving Barcelona suspects have identified an imam, who was killed in an explosion, as the ideologist of the extremist cell responsible for carrying out deadly attacks and planning others.

Only one of the four suspects acknowledged being part of the 12-member cell during proceedings at Spain's National Court on Tuesday.

Houli Chemlal's testimony is considered key to understanding the motivations of the 12-man cell as he is the lone survivor of a blast Wednesday that destroyed a house in Alcanar, south of Barcelona, where police believe the cell was preparing explosives for an even bigger attack on the city. Over 100 tanks of butane gas and materials to make TATP explosive were found at the house, police say.

Get Breaking News Delivered to Your Inbox

Chemlal told a judge that attackers were preparing bombs for an imam believed to be the leader of the cell to strike monuments in Barcelona, a source with Spain's judiciary said Tuesday.

The prosecutor has asked for Oukabir to be jailed without bail before trial -- along with the first suspect to testify, Mohamed Houli Chemlal. The other suspects were questioned were Mohammed Aalla and Said el Karib.

The judicial source, who spoke on condition of anonymity, said Aalla said his Audi A3 used in last week's attack in Cambrils had been stolen from him. And el Karib, the owner of a cybercafe in Ripoll, was he was only making an economic profit when he bought plane tickets for two members of the cell.

National Court prosecutor Ana Noe is asking for the four to be sent to prison without bail on preliminary charges of being part of a terrorist organization, homicide, causing havoc and dealing with explosives.

One suspect told the court 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.

The person said suspect Driss Oukabir denied being part of the attackers' cell. His brother Moussa was one of the five radicals shot dead Friday by police after a vehicle attack on pedestrians in Cambrils.

Oukabir was one of four attack suspects quizzed Tuesday at the court in Madrid by Judge Fernando Andreu and prosecutors. Andreu will decide whether the four should be jailed or released.

The person attending the hearing said Oukabir told the prosecutor his first version of events -- telling police that his documents were stolen by his brother -- was something he had done out of fear. The person spoke on condition of anonymity to discuss the hearing.

Oukabir, Aalla and el Karib were arrested Thursday in the northeastern town of Ripoll and Houli Chemlal in Alcanar for their alleged involvement in planning or carrying out two vehicle attacks on pedestrians -- one Thursday in Barcelona that left 13 dead and another in the nearby town of Cambrils early Friday that killed one person.

CBS News

Another person was killed by the alleged Barcelona van attacker as he fled. More than 120 people were injured, most in Barcelona.

The four were interrogated in the presence of lawyers provided for them by the court.

The Islamic State of Iraq and Syria (ISIS) has claimed responsibility for both attacks.

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 police who confronted him in a vineyard not far from the city that he terrorized.

Police said they had "scientific evidence" that Abouyaaqoub drove the van that barreled through Barcelona's crowded Las Ramblas promenade, mowing people down, then hijacked a car and fatally stabbed its driver while making his getaway.

Abouyaaqoub's brother and friends made up the rest of the 12-man extremist cell. Police said with Abouyaaqoub's death, the group's members were all dead or in custody.

Chemlal was born in Melilla, one of Spain's two North African coastal enclaves that have borders with Morocco. Spanish media say the other 11 suspects are mostly or all Moroccans that lived in Spain.