PHNOM PENH, Cambodia — Many of the foot soldiers for the Khmer Rouge remain in Cambodia’s remote reaches, each with a chronicle of the horror-soaked years in which Pol Pot and his Communist disciples turned the country into a deadly laboratory for agrarian totalitarianism.

Mea Chrun, a former bodyguard in the Khmer Rouge, lives in the jungle-choked hills of northern Cambodia, in Anlong Veng. He is matter-of-fact about the weight of the slaughter. “I think that one million people were killed,” he said. “Don’t say three million.”

On Friday morning — four decades after a total of at least 1.7 million people, a fifth of Cambodia’s population, were culled by execution, overwork, disease and famine — an international tribunal for the first time declared that the Khmer Rouge committed genocide against the Muslim Cham minority and Vietnamese.