Six of them were killed by police and two were killed in an explosion in the terrorists' bomb factory In Alcanar.
The probe into the August 17-18 attacks in Barcelona and Cambrils has suggested that ties of the alleged cell leader to other extremist cells and a criminal record for drug trafficking may have been missed because Catalan regional police didn't have information that was in the hands of central authorities.
The 51-year-old passed away on Sunday in the intensive care unit of Barcelona's Hospital del Mar, the regional health department said.
"There, with all of Catalan society and all of Spain... we will once again give a clear message of unity and condemnation of terrorism, and of love for the city of Barcelona", he added.
Five days ago, 22-year-old Morrocan, Younes Abouyaaqoub, the prime suspect of the deadly vehicle ramming incident which witnessed the killing of at least 14 people and injured more than 100 others in the bustling Las Ramblas area of Barcelona, was killed by Spanish police.
Barcelona's mayor Ada Colau has urged citizens to join a "massive rally" on Saturday to show their wholehearted rejection of violence. Authorities say 24 remain hospitalised, five in critical condition.
That attack has now killed 14 people, and two others died during the driver's getaway and in a separate auto and knife assault in the Catalan coastal resort of Cambrils.
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The Islamic State group has claimed the vehicle attacks in Barcelona and hours later in the coastal town of Cambrils that left 15 dead and over 120 wounded.
In Cambrils, five attackers climbed out of the overturned auto and were shot dead by police.
A separate anti-violence rally was held in the northern town of Ripoll, home to numerous attackers.
The massive march was led by #King Felipe Vi, Spanish Prime Minister Mariano Rajoy, and Carles Puigdemont, Catalonia's regional government head.
However, not everybody in the crowd was happy with their presence, as people said on Twitter that the monarch was booed.
Four other suspected terrorists appeared in court in Madrid last Tuesday.
Pugdemont commented that despite the "legitimate political disagreements" the eulogy to the victims had been dignified.