The 12 young men who formed the terror cell that carried out last week's terrorist attacks in Spain's Catalonia region had been indoctrinated into the extreme Takfir Wal-Hijra ("excommunication and exodus") sect of Salafi jihadism, counter-terrorism sources have told EL PAÍS.

The so-called takfiris comprise the most radical and violent strand of Salafi jihadism and figure in the European Union's list of terrorist organizations. They also represent the most dangerous form of jihadism because their members hide in plain sight.

Evidence suggests Aldelbaky es Satty, the imam who headed the Catalonia terror cell based in the Catalan town of Ripoll – and who died in an accidental explosion in a house being used as a base of operations by the group – indoctrinated its members into this form of Salafi jihadism that is very difficult for security forces to detect.

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