The skulls of more than 5,000 victims of the Khmer Rouge regime of 1975 to 1979 rest inside a Buddhist memorial stupa at the Choeung Ek Genocidal Center near Phnom Penh, Cambodia. Most have been smashed in or show puncture wounds. In order to save ammunition, the Khmer Rouge usually murdered their victims by bludgeoning them to death or slitting their throats. Choeung Ek is the best known of the more than 300 mass execution sites that were used by the Khmer Rouge and are now known as the Killing Fields. An estimated 2 million people died under the Khmer Rouge. At least 1.4 million of them are believed to have perished at Choeung Ek and other execution sites. March 1, 2012.