Spanish officials say one suspect reportedly involved in the Barcelona van attack was killed, on Friday.
Asked on the question and answer site who what he would do on his first day as absolute ruler of the world, Moussa Oukabir replied: "Kill all infidels".
Police do not believe that the teenager was the driver of the van in Las Ramblas on Thursday afternoon. Police believe the attacks could have been even worse. The Audi rammed into a police vehicle Catalan who was shot dead during a shoot-five "suspected terrorists".
On Friday they said they had detained a third suspect in Ripoll, the town where Driss Oukabir lived.
Spanish officials also warned the back-to-back vehicle attacks in Barcelona and a nearby resort were planned for a long time by an Islamic terrorist cell - and could have been far deadlier had its base not been destroyed by an apparently accidental explosion this week.
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The fourth man sought, Moussa Oukabir, thought to have been the van driver, was killed in the police shootout at Cambrils.
Officers have found "the remains of two different people, we are working to prove that they are two of these three people who have been identified", said Trapero.
Of the five attackers, two have been identified as Said Aallaa, 18, and Mohamed Hychami, 24.
The tweet said: "There is nobody held up in any bar in the center of Barcelona". Three of them were arrested in the northern town of Ripoll. They are aged between 21 and 34, and do not have a history of terror-related activities.
Four others have been arrested, one in Alcanar after Wednesday's explosion and three in the Catalan town of Ripoll after the Barcelona attack.
Spanish policemen walk in a cordoned off area after a van ploughed into the crowd, killing 13 persons and injuring over 80 on Las Ramblas in Barcelona on August 17, 2017.