Four top Khmer Rouge leaders have gone on trial at Cambodia's United Nations-backed war crimes court for genocide and other atrocities during the Maoist group's reign of terror in the 1970s.
The case, described as the most complex since the Nazi trials after World War 2, has been long awaited by survivors of the regime, which wiped out nearly a quarter of the population.
The elderly defendants, including "Brother Number Two" Nuon Chea and former head of state, Khieu Samphan, looked frail as they sat in the dock, the ABC reports.
They face charges including genocide, crimes against humanity and war crimes over the deaths of up to 2 million people from starvation, overwork, torture or execution during the Khmer Rouge's brutal 1975-79 rule.
The genocide charges relate specifically to the murders of Vietnamese people and ethnic Cham Muslims.
All four suspects, who also include ex-foreign minister Leng Sary and his wife and one-time social affairs minister Leng Thirith, deny the accusations.
"I am not happy with this hearing," said 84-year-old Nuon Chea, wearing his trademark sunglasses.
The defence lawyer for Nuon Chea, seen as the movement's chief ideologue, argued that the investigation into the case had lacked transparency and suffered from government interference.
"That judicial investigation was so unfair that the case should be stopped," Michiel Pestman said.
The complex proceedings, expected to take years, are seen as vital to healing the traumatised nation's deep scars.
"This trial is very important to find justice for those who died and for the survivors," said Khem Nareth, 56, who lost his mother and brother under the regime.