In a week full of programmes marking the forthcoming fifth anniversary of the 11 September attacks, this is probably the best. Compiled using eyewitness accounts and transcripts of conversations, 9/11: the Twin Towers tracks the events of that terrible day from inside the World Trade Center. It's a gripping, but of course often sad, litany of acts of bravery, and of resignation, too, as workers trapped within the doomed building realised they were going to die and made final phone calls to their loved ones. Firefighters who survived the onslaught recall trudging up smoke- filled stairwells, while office workers remember their perilous escapes. The atrocity is set within the context of a woeful catalogue of US security failures, highlighted in withering detail in the 9/11 Commission report, and how lessons were not learnt after previous al-Qaeda attacks on American targets. As one government official says, "We never even imagined it, therefore we weren't prepared."