After the attacks in Barcelona and Cambrils on 17th August last year, the Mossos d'Esquadra, the Catalan police, sent the National Audience court a report on the criminal records of the members of the cell. This didn't mention the 2010 arrest of the cell's ringleader, Abdelbaki Es Satty, because, according to the newspaper Ara, it wasn't recorded in the database the Catalan police had to work from.
Es Satty, who died in an accidental explosion of a house in Alcanar the day before the attack whilst the group prepared bombs they planned to use, was linked to the plot because of documentation in his name found in the ruins of the house. When the Mossos followed up on him, they didn't find his criminal history recorded in their database, even his time in prison for drug trafficking just years earlier.
"No record of arrest by any police force", that original report says, which does include the Mossos' arrests of another member of the cell, Driss Oukabir. Oukabir had been detained for crimes including robbery with violence, sexual abuse with penetration and mistreatment in the area of the home.