More than 200 people traveled to the Choeung Ek killing fields on the outskirts of the capital for a memorial service hosted by the opposition Sam Rainsy Party (SRP) and led in prayer by 50 Buddhist monks.
Men Yean, 53, was one of the mourners who attended the Choueng Ek ceremony. She wept as she recounted how six of her family had died under the Khmer Rouge's Democratic Kampuchea reign between 1975 and 1979, including one brother whose body was dumped in a mass grave at these very killing fields.
'I can never forget. I lost six of my family. I want to call on the United Nations to hold a trial for the people who killed them soon, before it is too late,' she said.
The Khmer Rouge is held responsible for the deaths of up to two million Cambodians through disease, starvation, torture, overwork and executions during its brief but bloody rule.
The ultra-Maoist movement took
Even the name Choeung Ek is a grisly reminder of the grim intentions of the Khmer Rouge. The name translates as 'champions', and a Buddhist stupa piled high with skulls is surrounded by mass graves filled mainly with the bodies of prisoners from the equally infamous S-21, or Toul Sleng detention and torture center - Pol Pot's secret jail.
Efforts to get a proposed joint UN-Cambodian government trial of former leaders underway continue to grind forward, but survivors and observers have warned that justice must be found soon or not at all if the mainly aging and ailing former leaders are ever to face the court.
Most prime candidates for trial still live freely in their communities. Others are already dead. The movement's supreme leader, Pol Pot, died without ever facing trial on April 15, 1998.
Opposition leader Sam Rainsy took the opportunity to urge authorities to hasten trial proceedings, saying that it was ironic that the nation's current phase of relative peace and political stability seemed to have dampened the fervour of some to hold a trial swiftly.