Salas came close to blowing his cover only once, when he met US journalist Jon Lee Anderson, who was in Venezuela promoting his Che Guevara biography. It was a nerve-racking encounter. "When he said he had been to Burkin and started naming people there, I feared my cover was gone."
Anderson remembers the meeting: "Burkin is an amazing place in the hills above Jenin. It is said to have the finest olive oil in the world. I remember thinking there was something odd [about Abdullah]; he was cautious around me and flustered, but Caracas is full of wackos. It didn't occur to me to think he was a plant."
Far from being made world-weary or cynical by his exposure to such violent worlds, Salas remains almost naively optimistic about the results of his investigations – which have spawned Spanish best-sellers, popular documentaries, even a feature film. After his previous two books, he says, he received letters from people who had given up being skinheads or frequenting prostitutes. "I hope for the same thing with this," he says. "In Spain and Latin America there are a lot of adolescents – many of whom I saw arrive at the mosque for the first time as children – who will feel the draw of violence in a few years' time."
So what conclusions does Salas draw from rubbing shoulders with international terror? His answer is coloured by the fact that half a dozen people he met during his investigation have since died – often violently. "I don't justify violence, but I can understand it. I never found any glamour or sophistication in that world, nor anyone especially intelligent – except for The Jackal. Terrorists really have only two ends – they either die or go to jail. You have to be a bit stupid to do that."