BARCELONA, Spain — Spanish authorities on Sunday continued their hunt for a 22-year-old suspect as well as two others in connection with the brutal vehicle attacks in Barcelona and a nearby coastal city late last week. A police official said that the terrorist cell had planned a “much more serious attack” that was probably thwarted by an accidental explosion Wednesday.

Authorities were looking for a fugitive they suspect may be Younes Abauyaaqoub, who may have been the driver of the van that plowed through crowds Thursday on Barcelona’s scenic Las Ramblas boulevard. The other two people whom police were seeking might have died Wednesday in the explosion.

Police said Sunday that they have linked three vans, a car and a motorcycle to the main fugitive in the attacks. The thoroughfare was packed with tourists and pedestrians, and 13 were killed. One additional victim was killed in a second vehicle attack hours later in the seaside resort of Cambrils, about 70 miles to the southwest.

Inspector Albert Oliva — the chief spokesman for the Catalan national police, the agency leading the investigation — reiterated on Spanish radio Sunday morning that the cell of 12 suspected terrorists has been dismantled. The cell was made up of Moroccans, all younger than 35, from or around a small town near the French border.

In an emotional plea Saturday on Spanish television, Abauyaaqoub’s mother, Hanno Ghanim, urged her son to turn himself in. “I prefer him going to jail before him dying,” she said.

Josep Lluís Trapero, head of the Catalan national police, did not confirm whether Abauyaaqoub is the suspected driver. “We do not know whether this person is in Spain,” he said. “If we did, we would go to him.”

Trapero said authorities are searching for three people from the cell: “We have found remains of two people. Four people have been detained. There is still one person missing.”

Spanish authorities and ordinary citizens alike struggled to make sense of a bizarre reality: that a group of childhood friends from the countryside — some of whom still lived with their parents and were too young to drive — could have planned such a deadly and complicated attack.

Nowhere was this questioning more acute than in Ripoll, the suspects’ home town, where their families and friends were taken aback by the news. Trapero said Sunday that the cell had probably been there for at least six months.

For many, it was difficult to believe that the group of young men could organized such a complicated operation — with multiple bases and targets — by themselves.

That was the principal question of Rashid Oukabir, a cousin of 17-year-old Moussa Oukabir, a suspect who was fatally shot by police early Friday during the vehicle attack in Cambrils. “Who is behind all this? Who is the big fish?” he said to The Washington Post on Saturday.

“It’s impossible these kids did all this on their own. Who helped them?”

At the moment, Trapero said, his department does not have any concrete information about how the group had been radicalized. However, he said, he believed the connection to the Islamic State was real. The militant group initially claimed responsibility for the violence in Spain, but the degree of its involvement in the planning remains unclear. On Saturday, the Islamic State published an expanded statement that contained factual errors. Such mistakes are not uncommon and should not exclude an Islamic State connection, security analysts said.

Trapero noted that at least one member of the cell had spent time in “the center of Europe,” though he said investigators were seeking additional information.

In Ripoll, the consensus among family members was that the young men fell under the sway of a visiting cleric who had possibly radicalized their sons, brothers and cousins.

In the Spanish media, all eyes are now on a suspect named as Abdelbaki Essati, who had served at a mosque in Ripoll and whose home was searched Saturday by the national Catalan police. Police said Sunday that Essati had not been connected to previous terrorism-related investigations, but that an unidentified friend of his had been implicated.

Police searched for DNA samples from his apartment, according to the Spanish newspaper El Pais, as they suspected Essati of having been one of two suspects killed in a Wednesday explosion, when butane and propane canisters likely intended for the Barcelona attacks detonated prematurely in the Spanish city of Alcanar. The identity of the second suspect killed in that blast remains unconfirmed.

“We know very clearly that this was the scene where they were preparing bombs for conducting one or two attacks in Barcelona,” Trapero said Sunday, noting that officers had discovered nearly 100 butane tanks as well as “ingredients” that linked to TATP, a signature Islamic State explosive.

The department’s “thesis,” Trapero said, was that the cell had planned a much more serious attack but had to abandon that after the accidental explosion. Trapero said that on Thursday, the attackers used only one van with only one person inside in Barcelona. He noted that police have since recovered three rented vans in connection with the attack, as well as the Audi A3 used in Cambrils and a motorcycle. Searches of the vehicles have produced “positive results,” he said.

In Barcelona, rocked by devastating attacks, life began to return to normal Sunday — albeit in an atmosphere of heightened anxiety and tightened security.

Carles Puigdemont, president of Catalonia, said Sunday that Barcelona had “rejected terrorism” and praised the city’s response to the crisis. “Normality has come back to Las Ramblas,” Puigdemont said to reporters, “and we are rejecting openly any sign of xenophobia or radicalism.”

Although much attention in the Spanish media has been paid to the Moroccan origins of the terrorists, Puigdemont was careful to defend the role of the minority group, numbering around 200,000, in the region. “The Moroccan people are integrated in Catalonia,” he said, “and they have made important contributions to the community.”

Prime Minister Mariano Rajoy and King Felipe VI of Spain attended a memorial Mass at Barcelona’s famous Sagrada Familia Basilica. Pope Francis relayed a message of condolence, expressing his “deep regret” at “such an inhuman action.”

Sunday will also see an FC Barcelona soccer match in the city, and police officials said security measures would be bolstered at the stadium.

“Security will be ensured as usual, as it’s always been done for football matches,” Trapero said. “Police stations always assess the risk and take measures accordingly.”