Michael Chertoff, former US Director of Homeland Security

Michael Chertoff was the man whose task it was to keep the USA safe. For four years he was the Director of Homeland Security under George W Bush and a leading figure in America's War on Terror. Michael Chertoff says that ten years after the September 11 attacks the world remains threatened by terrorist groups. So what have we learned over the last decade about how best to combat this ongoing threat? Michael Chertoff talks to Tim Franks.