Radicalization is a complex process given the fact that several factors interact in it. In order to gain an overview of these factors, a case study was performed of the cell that carried out the terrorist attacks in Barcelona and Cambrils. The 3N model of radicalization was used, which proposes three factors: needs, narratives and networks. The content of the order handed down by the National High Court and the police proceedings of Mossos d’Esquadra, the police force in Catalonia, were analysed to identify possible indicators of those three factors which may have contributed to the radicalization within the 17-A cell. The results showed the existence of different indicators such as providing a life purpose, giving personal significance, exposure to extremist propaganda materials, the assimilation of values, identity fusion and having a common cause. We conclude by stressing the importance of considering the interaction of multiple factors in understanding radicalization in all its complexity.