The US government has begun its investigation into how a well-armed group of men was able to kill the American ambassador to Libya in an assault on the US consulate in Benghazi on Tuesday.<br /><br />The attack came amid a protest against a YouTube movie made in America and aimed at insulting the prophet Muhammed. It was the first time a US ambassador was killed in the line of duty in 33 years.<br /><br />Ambassador Christopher Stevens had been the chief diplomatic liaison with Libyan rebels struggling to oust Muammar Gaddafi in 2011 and, prior to that, had served as the second-ranking diplomat in Libya during Gaddafi's reign.<br /><br />Patty Culhane reports from Washington DC.
