Phnom Penh, Cambodia (CNN) -- At least 1.7 million people -- nearly a quarter of Cambodia's population -- died under the 1975-1979 Khmer Rouge from execution, disease, starvation and overwork, according to the Documentation Center of Cambodia.
Four of the ultra-Maoist regime's former leaders are waiting to see if they will stand trial before a U.N.-backed tribunal for war crimes and crimes against humanity.
Kaing Guek Eav, alias Duch, the head of the infamous torture prison in the country's capital of Phnom Penh, has stood trial on charges including crimes against humanity.
He was convicted of war crimes and sentenced to 35 years in prison. Despite the sentence, Kaing Guek Eav, alias Duch, will serve no more than 19 years. The judge took off five years for the time Duch was illegally detained before the United Nations-backed tribunal was established, and another 11 years for the time he has already served behind bars.
The verdict came more than 30 years after the fall of the regime.
1970: Marshal Lon Nol stages a coup, forcing Prince Norodom Sihanouk out of power. Sihanouk is aligned with the Khmer Rouge, an ultra-Maoist group building up a following in the countryside
April 17, 1975: The Khmer Rouge seize Phnom Penh, completing their taking over of the country. The city's inhabitants are forced to leave the capital, heading out to rural areas. Some 2 million people are forced out of Cambodia's urban centers
Late 1977: Fighting breaks out between Vietnam and Cambodia
May 25, 1978: Khmer Rouge purges East Zone.
January 7, 1979: The Vietnamese take Phnom Penh, beginning 11 years of Vietnamese occupation. The Khmer Rouge move west. Some Cambodians celebrate January 7 as a liberation day from the Khmer Rouge, while others mark it as the start of Vietnamese occupation
1979: A genocide tribunal in Phnom Penh finds Pol Pot and Ieng Sary guilty of genocide. Neither appeared in court or served any sentence
1982: Triparty coalition government forms, consisting of Prince Sihanouk, who was exile in China, the Khmer Rouge and non-communist leader Son Sann to create the Triparty Coalition Government. Vietnam helps establish a new government led by Heng Samrin
1990: Vietnamese troops withdraw from Cambodia
October 23, 1991: Paris peace talks. A peace accord among all Cambodian parties is signed. They approve holding a national election under the supervision of the United Nations Transitional Authority in Cambodia. The Khmer Rouge boycott the polls and won't demobilize their forces.
May 23-28, 1993: The U.N.-supervised elections are held. The part of one of the king's sons, Ranariddh, wins but the Cambodian People Party sought an equal share of power. Hun Sen of the CPP and Ranariddh are appointed co-prime minister. Khmer Rouge soldiers continue to wage guerrilla war.
1996: King Norodom Sihanouk pardons top cadre Ieng Sary's genocide sentence from the 1979 genocide tribunal
1997: Khmer Rouge try Pol Pot for crimes allegedly committed within the regime after 1979. Cambodia asks the U.N. to help create a court to prosecute the surviving top leaders of the Khmer Rouge
1998: Pol Pot dies. Civil war ends in Cambodia
1999: Considered the end of the Khmer Rouge
2001: Cambodia's National Assembly passes a law to create a court to try serious crimes committed during the Khmer Rouge regime
2003: Agreement reached with the U.N. on how the international community would help and participate in the Extraordinary Chambers in the Courts of Cambodia. The pact was amended in 2004
June 2007: Court becomes fully operational
Nov 20, 2007: Pre-trial chamber opens its first public hearing on an appeal by Duch, Khmer Rouge head of the S-21 prison where some 14,000 people died, against his detention
July 26, 2010: Verdict in Duch case expected
Sources: Cambodia Tribunal Monitor (David Scheffer, Khamboly Dy), Extraordinary Chambers in the Courts of Cambodia, United Nations