US remembers 9/11 five years on [multiple clips]

Sombre ceremonies have been held in the US on the fifth anniversary of the devastating 11 September attacks which killed nearly 3,000 people. Survivors of the attack on the Pentagon reflect on what has changed in the last five years -- and what has not. After the attacks, many commentators and political leaders declared that the world had changed for ever. Five years on, what exactly has changed?