A timeline of the Khmer Rouge regime and its aftermath

Miranda Leitsinger, CNN, and Casey Tolan, for CNN

Updated 0323 GMT (1123 HKT) April 17, 2015

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Cambodian and international journalists watch a live video feed showing the verdicts in the trial of former Khmer Rouge leader "Brother Number Two," Nuon Chea, and former Khmer Rouge head of state Khieu Samphan, August 7, 2014.

Photos: Cambodia's bloody past

Cambodia's bloody past – Cambodian and international journalists watch a live video feed showing the verdicts in the trial of former Khmer Rouge leader "Brother Number Two," Nuon Chea, and former Khmer Rouge head of state Khieu Samphan, August 7, 2014.

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A Cambodian man Khieu Samphan on a television during the trial at the Extraordinary Chamber in the Courts of Cambodia (ECCC) in Phnom Penh on August 7. He and Nuon Chea were found guilty of crimes against humanity and sentenced to life in prison.

Photos: Cambodia's bloody past

Cambodia's bloody past – A Cambodian man Khieu Samphan on a television during the trial at the Extraordinary Chamber in the Courts of Cambodia (ECCC) in Phnom Penh on August 7. He and Nuon Chea were found guilty of crimes against humanity and sentenced to life in prison.

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Known as Brother Number Two, Nuon Chea was considered Khmer Rouge leader Pol Pot's right hand man. This is an image from court in 2011.<br />

Photos: Cambodia's bloody past

Cambodia's bloody past – Known as Brother Number Two, Nuon Chea was considered Khmer Rouge leader Pol Pot's right hand man. This is an image from court in 2011.

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As the former head of state for the Khmer Rouge, Khieu Samphan occupied a number of key roles as the government tortured, starved and killed its people.

Photos: Cambodia's bloody past

Cambodia's bloody past – As the former head of state for the Khmer Rouge, Khieu Samphan occupied a number of key roles as the government tortured, starved and killed its people.

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This undated photo, which may have been taken in 1989, shows Pol Pot, the former leader of the Khmer Rouge. He was under house arrest when he died in 1998 and never faced charges for the slaughter under his reign.

Photos: Cambodia's bloody past

Cambodia's bloody past – This undated photo, which may have been taken in 1989, shows Pol Pot, the former leader of the Khmer Rouge. He was under house arrest when he died in 1998 and never faced charges for the slaughter under his reign.

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At least 1.7 million people were killed under the Khmer Rouge's brutal regime, which controlled Cambodia from 1975 to 1979. This photo shows open mass graves in 1979.

Photos: Cambodia's bloody past

Cambodia's bloody past – At least 1.7 million people were killed under the Khmer Rouge's brutal regime, which controlled Cambodia from 1975 to 1979. This photo shows open mass graves in 1979.

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Khmer Rouge guerilla soldiers wearing black uniforms drive into Phnom Penh in April 1975, as Cambodia falls under the control of the Khmer Rouge.

Photos: Cambodia's bloody past

Cambodia's bloody past – Khmer Rouge guerilla soldiers wearing black uniforms drive into Phnom Penh in April 1975, as Cambodia falls under the control of the Khmer Rouge.

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A woman cries next to a dead body in April 1975 in Phnom Penh, after the Khmer Rouge enter the Cambodian capital and establish the government of Democratic Kampuchea (DK).

Photos: Cambodia's bloody past

Cambodia's bloody past – A woman cries next to a dead body in April 1975 in Phnom Penh, after the Khmer Rouge enter the Cambodian capital and establish the government of Democratic Kampuchea (DK).

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Historical, undated photo of Nuon Chea. He held a number of positions during the regime's rule, including a short stint as acting prime minister.

Photos: Cambodia's bloody past

Cambodia's bloody past – Historical, undated photo of Nuon Chea. He held a number of positions during the regime's rule, including a short stint as acting prime minister.

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Historical, undated photo of Khieu Samphan. During his trial, Khieu Samphan expressed remorse, claiming he was unaware of the full extent of the atrocities. He became the public face of the Khmer Rouge as it sought international credibility after its fall.

Photos: Cambodia's bloody past

Cambodia's bloody past – Historical, undated photo of Khieu Samphan. During his trial, Khieu Samphan expressed remorse, claiming he was unaware of the full extent of the atrocities. He became the public face of the Khmer Rouge as it sought international credibility after its fall.

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A Cambodian man sits in Choeung Ek Killing Fields near a tree that was used to beat children to death during the Khmer Rouge regime on August 6, 2014 in Phnom Penh, Cambodia.

Photos: Cambodia's bloody past

Cambodia's bloody past – A Cambodian man sits in Choeung Ek Killing Fields near a tree that was used to beat children to death during the Khmer Rouge regime on August 6, 2014 in Phnom Penh, Cambodia.

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A Cambodian man stands by a wall of photographs of prisoners of the Khmer Rouge regime in one of the rooms of Tuol Sleng prison, also known as S-21, on August 6 in Phnom Penh.

Photos: Cambodia's bloody past

Cambodia's bloody past – A Cambodian man stands by a wall of photographs of prisoners of the Khmer Rouge regime in one of the rooms of Tuol Sleng prison, also known as S-21, on August 6 in Phnom Penh.

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Cambodian citizen Sam Vishna looks at a collection of skulls that make up a map of Cambodia at Tuol Sleng Prison Museum in Phnom Penh in 1998.

Photos: Cambodia's bloody past

Cambodia's bloody past – Cambodian citizen Sam Vishna looks at a collection of skulls that make up a map of Cambodia at Tuol Sleng Prison Museum in Phnom Penh in 1998.

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Photos: Cambodia's bloody past

Cambodia's bloody past – Cambodian Buddhist monks bless victims' skulls at the Choeung Ek Killing Fields memorial in Phnom Penh on April 17, 2008.

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Photos: Cambodia's bloody past

Cambodia's bloody past – Cambodian Sao Phen prepares skulls and bones of victims of the Khmer Rouge inside a stupa in Kandal province in 2009.

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A Cambodian woman looks at portraits of victims of the Khmer Rouge at the Tuol Sleng genocide museum in Phnom Penh on November 17, 2011.

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Cambodia's bloody past – A Cambodian woman looks at portraits of victims of the Khmer Rouge at the Tuol Sleng genocide museum in Phnom Penh on November 17, 2011.

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Story highlights

Khmer Rouge ruled from 1975 to 1979
Leader was Pol Pot who died in 1998
Charges brought against five top leaders
"Duch" sentenced to life, two verdicts pending

(CNN)At least 1.7 million people -- nearly a quarter of Cambodia's population -- were killed by execution, disease, starvation and overwork under the Khmer Rouge's brutal rule from 1975 to 1979.

Three of the ultra-Maoist regime's former leaders have been found guilty for crimes against community by a U.N.-backed tribunal.

On Thursday, guilty verdicts were handed down to Nuon Chea, otherwise known as Brother Number Two, and Khieu Samphan, the one-time President of Democratic Kampuchea, as Cambodia was known.

Kaing Guek Eav, alias Comrade Duch, the head of an infamous torture prison, was convicted of crimes against humanity in 2010. He was ultimately sentenced to life in prison in 2012, more than 30 years after the fall of the regime.

Here's a timeline of the Khmer Rouge regime and the long path to bring its leaders to justice:

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 two 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. A royalist party lead by one of the king's sons, Ranariddh, wins a plurality and forms a coalition government with the Cambodian People's Party. Ranariddh and Hun Sen of the CPP 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: The Khmer Rouge tries 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 is 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: The court becomes fully operational.

November 20, 2007: The pre-trial chamber opens its first public hearing on an appeal by Duch, the Khmer Rouge head of the S-21 prison, where some 14,000 people died.

July 26, 2010: Duch is found guilty for war crimes, crimes against humanity, murder and torture, and sentenced to 35 years in prison.

February 3, 2012: Duch's sentence extended to life in prison.

August 7, 2014: Nuon Chea, otherwise known as Brother Number Two, and Khieu Samphan, the one-time President of Democratic Kampuchea, are found guilty and sentenced to life in prison.

Sources: Cambodia Tribunal Monitor (David Scheffer, Khamboly Dy), Extraordinary Chambers in the Courts of Cambodia, United Nations