Catalan interior minister Joaquim Forn said "everything indicates" Morrocan Younes Abouyaaquoub was behind the wheel during the attack on Las Ramblas.
Abouyaaqoub, who has reportedly fled into France on foot, is believed to be the only member of the 12-strong terror cell still on the run.
The atrocities in Barcelona and the seaside town of Cambrils left 14 innocent civilians dead and around 130 injured.
Five members of the cell were shot dead by police after they rammed a car into a group of pedestrians in Cambrils, killing a woman and injuring six others in the early hours of Friday morning.
Moussa Oukabir, aged 17 or 18, Said Aallaa, 19, and Mohamed Hychami, 24, were among those killed by officers.
Footage of the assailants lying dead on the ground showed they had been wearing fake suicide belts.
It is believed two of 12-man terror cell were killed in an explosion on Wednesday at the house in Alcanar where the terror plot was hatched.
Four others remain in custody.
The men, aged 21, 27, 28 and 34, were arrested in connection with the attack. Three are Moroccan and one is Spanish.
Officials believe the terror group behind the attacks were plotting much deadlier carnage using explosives favoured by Islamic State militants.
Three vehicles were rented using the credit card of Abouyaaqoub and police believe the group wanted to load the vans with explosives for a big attack, but were forced to change their plans after the house in Alcanar blew up.
The group is said to have stored more than 100 gas tanks and explosive ingredients at the house.
The investigation is also focusing on a missing imam who police believe could have been killed by the explosion.
Abdelbaki Es Satty is suspected of radicalising the 12-man terror cell.
His home in Alcanar was raided by police on Saturday.
Spanish newspaper El Pais said Abdelbaki Es Satty was imam at one of the two mosques in Ripoll, in the north-east of Spain near to the French border and around 62 miles from Barcelona.
All of the main suspects are believed to have lived in the small town, which has a Muslim community of around 500 people.
Es Satty was reportedly friends and acquaintances with some of those jailed of the Madrid train bombings in 2004, having spent four years in prison himself for drug trafficking and breaking Spanish immigration laws, the newspaper said.
He also had spent several months looking for work in the Vilvoorde district north of Brussels, in Belgium, the region's mayor Hans Bonte told Belgian newspaper De Morgen.
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.
Police are investigating his role in radicalising the younger members of the cell before he was reportedly killed in the explosion in Alcanar, 124 miles south of Barcelona.