Pran and New York times reporter Sydney Schamberg stayed behind Cambodia to cover the fall of the capital Phnom Penh to Khmer Rough. Sydney and other foreign reporters were allowed to leave the country, but Pran was not. The Khmer Rough were killling the intellectual citizens so Pran hid that he was educated and pretended to be a taxi driver. Pran faced being tortured and starving for four years and escaped and while his journey he encountered corpses and skulls and made the phrase "killing fields".
When he reached Siem Reap the Vietnamese made him village chief. But he was afraid that the Vietnamese would find out his US ties, and so Pran escaped to Thailand on October 3rd 1979.
At that time Vietnam overthrew the Khmer Rouge in December 1978