As soon as The Khmer Rouge came to power, with the fall of Phnom Penh at the time, the regime arrested and then executed almost everyone suspected of connections with the former government or with foreign governments, including professionals and intellectuals. Ethnic Vietnamese, ethnic Thai, ethnic Chinese (except for those already prominent among the Khmer Rouge themselves), ethnic Chams (Muslim Cambodians), Cambodian Christians (most of whom were Roman Catholic, along with its Priesthood) and the Buddhist monkhood were the demographic targets of persecution. As a result, Pol Pot is sometimes described as "the Hitler of Cambodia" and "a genocidal tyrant." Martin Shaw described the Cambodian genocide as "the purest genocide of the Cold War era."
According to Michael Vickery, 750,000 people in Cambodia in a population of about 7 million died due to disease, overwork, and political repression. However, many scholars disregard his claims because the number of victims of execution found in the mass graves is higher than his estimate for deaths from all causes during the rule of the Khmer Rouge and the civil war combined. The most widely accepted estimate, from scholar Ben Kiernan, is that about 1.7 million people were killed. It is described by the Yale University Cambodian Genocide Program as, "one of the worst human tragedies of the last century." Researcher Craig Etcheson of the Documentation Center of Cambodia suggests that the death toll was between 2 and 2.5 million, with a "most likely" figure of 2.2 million. After 5 years of researching some 20,000 grave sites, he concludes that, "these mass graves contain the remains of 1,386,734 victims of execution." Execution is believed to have accounted for about 30-50% of the death toll. This would indicate 2.5 to 3 million deaths, but normal mortality over this period would have accounted for about 500,000 deaths—subtracting this from the total sum, we arrive at Etcheson's range for the number of "excess" deaths attributable to the Khmer Rouge regime.[9] A UN investigation reported 2-3 million dead, while UNICEF estimated 3 million had been killed.[10] Even the Khmer Rouge acknowledged that 2 million had been killed—though they attributed those deaths to a subsequent Vietnamese invasion. By late 1979, UN and Red Cross officials were warning that another 2.25 million Cambodians faced death by starvation due to “the near destruction of Cambodian society under the regime of ousted Prime Minister Pol Pot,” who were saved by American and international aid after the Vietnamese invasion.
Although Pol Pot is credited with killing 1/4 of the Cambodian population, there is debate as to whether or not this constitutes genocide under international law. Moreover, there is a separate debate as to whether or not the persecution of minorities by the Khmer Rouge constituted genocide.
Cambodia's ethnic minorities constituted 15 percent of the population in pre-Khmer Rouge era. Of the 400,000 Vietnamese who lived in Cambodia before 1975, some 150-300,000 were expelled by the previous Lon Nol regime. When Pol Pot's Khmer Rouge came to power, there remained about 100-250,000 Vietnamese in the country. Almost all of them were repatriated by December 1975. Some argue that the Khmer Rouge had no intent to cause serious mental and physical harm to the Vietnamese during the sun repatriation process.
The Chinese community (about 425,000 people in 1975) was reduced to 200,000 during the next four years. In the Khmer Rouge's Standing Committee, four members were of Chinese ancestry, two Vietnamese, and two Khmers. Some observers argue that this mixed composition makes it difficult to argue that there was an intent to kill off minorities. R.J. Rummel, an analyst of political killings, argues that there was a clear genocidal intent:
Not only did the Khmer Rouge run amok massacring their people, but also everywhere the Khmer Rouge tried to destroy the very heart of peasant life. Hinayana Buddhism had been a state religion, and the priesthood of monks with their saffron robes was a central part of Cambodian culture. Some 90 percent of Cambodians believed in some form of Buddhism. Many received a rudimentary schooling from the monks, and many young people became monks for part of their lives. The Khmer Rouge could not allow so powerful an institution to stand and therefore set out with vigor to destroy it. They exterminated all leading monks and either murdered or defrocked the lesser ones. One estimate is that out of 40,000 to 60,000 monks only 800 to 1,000 survived to carry on their religion. We do know that of 2,680 monks in eight monasteries, merely seventy were alive in 1979.
As for the Buddhist temples that populated the landscape of Cambodia, the Khmer Rouge destroyed 95 percent of them, and turned the few remaining into warehouses or allocated them for some other degrading use. Amazingly, in the very short span of a year or so, the small gang of Khmer Rouge wiped out the center of Cambodian culture, its spiritual incarnation, its institutions. This was an act of genocide within the larger Cambodian democide, and it was not the only one. In most if not all the country, simply being of Chinese, Vietnamese, Thai, or Lao ancestry meant death. As part of a planned genocide campaign, the Khmer Rouge sought out and killed other minorities, such as the Moslem Cham. In the district of Kompong Xiem, for example, they demolished five Cham hamlets and reportedly massacred 20,000 that lived there; in the district of Koong Neas only four Cham apparently survived out of some 20,000.
The cadre threw the Cham Grand Mufti, their spiritual leader, into boiling water and then hit him on the head with an iron bar. They beat another leader, the First Mufti, to death, tortured and disemboweled the Second Mufti, and murdered by starvation in prison the Chairman of the Islamic Association of Kampuchea (Cambodia). Overall, the Khmer Rouge annihilated nearly half--about 125,000--of all the Cambodian Cham. As to the other minorities, the Khmer Rouge also slaughtered about 200,000 ethnic Chinese, almost half of those in Cambodia--a calamity for ethnic Chinese in this part of the world unequaled in modern times--additionally, they murdered 3,000 Protestants and 5,000 Catholics; around 150,000 ethnic Vietnamese (over half); and 12,000 ethnic Thai out of 20,000. One Cambodian peasant, Heng Chan, whose wife was of Vietnamese descent, lost not only his wife, but also five sons, three daughters, three grandchildren, and sixteen of his wife's relatives. In this genocide, the Khmer Rouge probably murdered 541,000 Chinese, Chams, Vietnamese, and other minorities.