"Betrayal of the treacherous is loyalty in the eyes of God. I betrayed a bunch of criminals, it's as simple as that" - the words of one of MI6's most important spies in the war on terror, Aimen Dean.
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Aimen Dean, with Paul Cruikshank and Tim Lister, tells his story in full in the book 'Nine Lives: My time as MI6's top spy inside al-Qaeda'.
He worked with Al Qaeda's master bombmaker in a training camp in Afghanistan in the nineties.
But after witnessing what he described as wanton acts of cruelty and blood lust, he says he became disillusioned and became a crucial asset for British intelligence.