The Isis terror group has claimed responsibility for the attacks in Spain.
Local media said the dead man was Younes Abouyaaqoub, the 22-year-old Moroccan wanted for the Las Ramblas outrage. They believe Abouyaaqoub took the auto, rammed into officials at a police checkpoint in the city and then abandoned the vehicle with the dead body in it.
Police said that Abouyaaquob had stabbed Perez to death when he stole his auto to use as a getaway vehicle after the van attack.
Abouyaaqoub, who may have fled to France, is believed to be the only member of the 12-strong terror cell still on the run. His mother, Hannou Ghanimi, had appealed for him to surrender, saying she would rather see him in prison than end up dead. "These were people who avoided problems, kept their distance when they saw a fight", Saber Oukabir, a cousin of two of the attackers, said.
"They were preparing one or several attacks in Barcelona and an explosion in Alcanar stopped this as they no longer had the material they needed to commit attacks of an even bigger scope", Josep Lluis Trapero of Catalonia's police said. He loved exploring "new places", she said, "and a proper-sized pint".
In little more than a year, Islamist militants have used vehicles as weapons to kill almost 130 people in France, Germany, Britain, Sweden and Spain. They are now being taken to the high court in Madrid, which has jurisdiction over terrorism matters. They were killed by the police during a second attack in the seaside town of Cambrils early on Friday.
A auto crashed into passers-by there and attackers got out to try and stab people.
Police said they had "scientific evidence" that Younes Abouyaaqoub, 22, drove the van that barreled through Barcelona's crowded Las Ramblas promenade, killing 13 people on Thursday, then hijacked a vehicle and fatally stabbed its driver while making his getaway.
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Of the 120 injured on Las Ramblas, nine remain in a critical condition in hospital. The cell had collected 120 gas canisters and were planning a "much more serious attack" that was probably thwarted by an accidental explosion on Wednesday. Abouyaaqoub is still being sought by police.
Twenty-four hours after the Alcanar blast, the police believe that the town may have been where the attacks were planned - news that shocked local residents.
Abouyaaqoub began showing more religiously conservative behaviour within the past year, according to family members in his native Morocco.
Vilvoorde is known for jihadi activity and police were said to have contacted the Catalan department of justice and were told Es Satty had no links to extremist violence.
Three of the men were killed in Cambrils.
Investigators are seeking to unravel the role of the imam, who is believed to have radicalized numerous youths in a small town called Ripoll at the foot of the Pyrenees.
Spanish political leaders from all the main parties were also due to meet later to review security measures as part of cross-party efforts to unite on anti-terrorist efforts.