The man who trained the Bali bombers has turned his back on terrorism and is working with police. His extraordinary story is told in the second of Peter Taylor's investigations to mark the fifth anniversary of 9/11. Taylor visits South East Asia to explore how the region has fought al-Oaeda's allies and those responsible for twice bombing Bali. Nasir Abas has rejected terrorism to inform on his former comrades, give evidence against them in court and try to persuade them to change sides. He has become a devastating new weapon in the war against al-Qaeda's affiliates. But will others follow?

Terror vision: page 18