In the weeks before terrorists ploughed a van through pedestrians on Las Ramblas boulevard, a cell of jihadists inspired by ISIS travelled repeatedly to France, according to footage and documents analysed by Fernando Reinares and Carola García-Calvo from the Royal Institute’s Program on Global Terrorism in Madrid.
The terror group recorded footage of the Eiffel Tower, which led Mr Reinares and Ms García-Calvo to believe the jihadis had planned to strike the Eiffel Tower with a “potentially more deadly operation”.
They said: “The existing evidence indicates the terrorist cell had planned a far more ambitious and potentially more deadly operation.
“Considering the lethal resources assembled by the terrorists and their lethal intent, the death toll could have reached hundreds had they not accidentally blown up their bomb factory.”
According to Mr Reinares and Ms García-Calvo the terror group’s plans were derailed a day before the Barcelona attacks after an abandoned house where they were storing explosive powder in the Spanish town of Alcanar exploded.
The explosion demolished the building, burying two of the cell’s 10 members and injuring a third.
The terror experts claim the explosion prompted the other cell members to move up the timings of attacks on Barcelona and Cambrils.
Inside the ruins of the group’s explosives factory, investigators later recovered 500 litres of acetone – a solvent used in cleaning supplies– and 340 litres of hydrogen peroxide.
The two chemicals are the raw ingredients used to make triacetone triperoxide, or TATP, which has become the signature explosive used by ISIS.
Investigators estimate that the terrorist cell had enough chemicals to make 200 to 250 kilograms (440 to 550 pounds) of TATP – which is more than 10 times the amount used in the Brussels attack in March 2016.
The suitcase bombs that killed 32 people at the Brussels airport and injured more than 320 reportedly weighed less than 20 kilograms each.
Younes Abouyaaqoub, who drove the van in the attack at Las Ramblas, visited France at least three times from July to December 2016, and again on August 11 and 12, 2017, just days before the attack.
In his last trip to Paris, he stayed at a hotel in Malakoff, located around four miles (6km) from the Paris suburb of Villejuif, where French authorities later discovered a TATP lab run by men who had been making phone calls to Syria.
The investigators, according to the study, also recovered a notebook in the ruins of the Alcanar property inscribed with the name of Abdelbaki Es Satty, the oldest member of the cell and what the researchers presume was the ringleader and recruiter.
In a sheet inside the notebook, they found a handwritten note in Arabic describing the cell members as “soldiers of the Islamic State in the land of al-Andalus”.
Within hours of the first attack, and again after the second, ISIS’s news agency, Amaq, claimed credit, describing the attackers as “soldiers of the Islamic State.”
However, authorities have said so far there is no evidence that the terror cell was being trained by ISIS operatives abroad.
In addition to the footage of the Eiffel Tower, a mobile phone used by one of the terror cell’s member included searches on Google Maps for several locations in Spain, including the Sagrada Familia church in Barcelona and the Camp Nou soccer stadium, which the researchers believe may also have been targeted.
Spanish officials reportedly warned their French counterparts about recovered the footage of the Eiffel Tower soon after the Barcelona attack.
According to Mr Reinares and Ms García-Calvo, the French government also determined that the cell may have intended to strike Paris and this prompted a glass fence to be installed around the Eiffel Tower.
The two experts published their findings in the CTC Sentinel, the publication of the Combating Terrorism Center based in New York.
And it is based on interviews with investigators, a review of court proceedings and an analysis of videos, images and other materials recovered from the scenes.