Forty years ago the CIA recruited and trained a group of hill people in Laos to help fight the north Vietnamese in what became known as the "secret war". The Hmong fought as guerrilla jungle units, blocking the Ho Chi Minh Trail and rescuing downed US pilots. More bombs were dropped on Laos during that time than in the whole of Western Europe in World War Two. After the communists took control of Laos the Hmong became targets for persecution and many fled to Thailand. Now they are being sent back and feel abandoned by the US, and believe they will be killed. Alastair Leithead reports on the Hmong's struggles.