Police say Abouyaaqoub was wearing what appeared to be a belt of explosives when he was shot down.
He was cornered in Subirats, about 30 miles west of Barcelona.
In Cambrils, a car crashed into passers-by and its occupants got out and tried to stab people. Neighbors said they did not suspect any wrongdoing at the property.
El Mundo newspaper reported that Satty had struck up a friendship in prison with Rachid Aglif, who is serving an 18-year sentence over the 2004 Madrid train bomb attacks, which killed 191 people.
Officials believe the terror group behind the attacks were plotting much deadlier carnage using explosives favoured by Islamic State militants.
On Monday, police said they believed Imam Abdelbaki Es Satty was one those who died in Alcanar. Las Ramblas is filled with about a dozen ever-widening pavement tributes of candles, flowers and messages of sympathy and defiance.
Police now consider that the death toll from the attacks stands at 15, including the Spanish man stabbed in his car as he was parking. He then hijacked a car and killed the driver - who police have confirmed as the 15th victim.
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Perez was parking his car, a Ford Focus, in a lot between 6.10pm and 6.20pm local time.
The suspect ran over a police officer as the car evaded the checkpoint.
New CCTV footage appears to show him fleeing the scene of the attack on foot.
Spanish papers El Pais and La Vanguardia said they had seen images of the man leaving Las Ramblas then crossing through La Boqueria food market, another tourist attraction, before disappearing. The manhunt for him reaches well beyond Spain's borders.
Regional authorities said that 48 people were still hospitalised from both attacks, eight of them in critical condition.
Abouyaaqoub was believed to be the lone attacker on the run.
On Monday, mourners were still weeping and hugging each other as they visited the main memorial site of the Barcelona attack.
Four others have been arrested in connection with the attacks: Driss Oukabir, 28, Mohamed Houli Chemlal and Sahal al-Karib, 34, and Mohammed Aalla, 27.
Abouyaaqoub allegedly abandoned the van after zig-zagging down Las Ramblas avenue at high speed, police have said. "Because Barcelona is strong and they will not be able to prevail with us".
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