Three men took the stand at a Spanish court on Tuesday as they went on trial for helping the jihadists behind the 2017 attacks in Barcelona and a nearby town that killed 16 people and left 140 wounded.
The Islamic State group said they carried out the attacks - one of which involved a van ramming people in the city centre - on August 17 and 18, part of a string of jihadist attacks carried out that year across Europe.
Although all six perpetrators were shot dead by police, many questions remain unanswered with both victims and prosecutors hoping the trial at Spain's National Court will shed light on how it all unfolded.
Some 235 witnesses will be called during the trial at a court in San Fernando de Henares near Madrid, which will run until December 16.
While none of the trio are charged with direct responsibility, they are in the dock for helping the attackers, one of whom rammed a van into pedestrians on Barcelona's Las Ramblas boulevard on a busy Saturday in August, killing 14.
The driver fled and killed another person before being shot dead several days later.
In the early hours of Sunday morning, five others rammed pedestrians on the seafront in Cambrils, 100 kilometres (60 miles) further south, and fatally stabbed a woman before being shot dead by police.
Main defendant Mohamed Houli Chemlal refused to answer questions in court about the facts, pointing to statements given in the days after the attacks.
He said he was willing to cooperate and when asked if he was sorry said: "Obviously."
Prosecutors then showed footage of the cell preparing an explosive belt.
Driss Oukabir, 31, whose brother was one of the attackers and is accused of renting the van used in Barcelona, denied being part of a terror cell and said he "wasn't religious".
He told the court his brother and Barcelona attacker Younes Abouyaaqoub, 22, had asked if he would hire a van for them as a favour "for moving house, because they weren't old enough to rent one".
Testifying last, Said Ben Iazza, 27, admitted lending his ID card and vehicle to two men whom he knew as business customers who said they were going to buy cleaning products.
He denied knowing they wanted to make explosives and, like Oukabir, insisted he didn't know Abdelbaki Es Satty, the 44-year-old imam who radicalised the young men in Ripoll, their hometown at the foot of the Pyrenees.
High-profile target
Chemlal and Oukabir are both on trial for membership of a jihadist group, manufacturing and possessing explosives and conspiracy to wreak havoc, while Ben Iazza is charged with collaborating with the group.
Prosecutors have called for a 41-year jail sentence for Chemlal and 36 years for Oukabir, while Ben Iazza faces eight years behind bars.
During the investigation, Chemlal admitted the initial plan was to hit targets like Barcelona's Sagrada Familia basilica, with police also finding documents relating to Barcelona's Camp Nou football stadium and the Eiffel Tower in Paris.
But on Friday 16 August, an accidental explosion at a house in Alcanar, a town between Barcelona and Valencia where the cell had been preparing explosives, pushed them to hurriedly improvise the weekend attacks.
Chemlal survived the blast, but it killed the imam and another person. Both Oukabir and Ben Iazza denied being in Alcanar.
Many questions, few answers
Antonio Guerrero, a lawyer for the AVT terror victims' association said all three should be in the dock for "terrorist murder".
"In our opinion, the fact that they didn't actually take part in the criminal activity of murder does not mean we can't prosecute and convict them," he said as he went into the courtroom.
"In our opinion, they were part of the cell."
Lawyer Jaume Alonso-Cuevas said the aim of the trial was to get to the truth.
"There are too many questions that haven't been answered," he said.
"We want the state to be accountable for not regulating the sale of explosives purchased by the cell to prepare for attacks," he added, saying it was unthinkable that anyone "could go out and buy 250 kilogrammes (550 pounds) of material to make explosives."