The trial of former Khmer Rouge leaders is a chance for the regime's victims to overcome their lingering trauma, a psychological expert told Cambodia's UN-backed tribunal Tuesday.

Dr Chhim Sotheara was testifying at the trial of Duch, whose real name is Kaing Guek Eav and who stands accused of overseeing the torture and execution of roughly 12,000 people at Tuol Sleng prison during the regime's 1975-79 rule.

But the expert, who is director of Cambodia's Transcultural Psycho-social Organisation, noted that the victims' trauma seemed to reoccur after they observed the court proceedings. The denial by some Khmer Rouge leaders of their roles in the atrocities also created more pain for the victims, he said.

Chhim Sotheara said that people were traumatised throughout the nation after the Khmer Rouge destroyed the country's infrastructure and created an "environment of fear".

He told the court that Cambodians could cope with their three-decade-old trauma only when justice had been served and the truth behind regime was revealed.

"The trial of the former leaders of the Khmer Rouge is an opportunity for the victims who have suffered and who have been traumatised for many years to overcome their trauma through justice," he said.

"It will be very helpful to heal the wounds, the suffering of those victims," he added.

Chhim Sotheara told the court that for every five Cambodians, two had developed trauma, while 14 percent of country's population aged over 18 had experienced post-traumatic stress disorder.

Led by Pol Pot, who died in 1998, the Khmer Rouge emptied Cambodia's cities in a bid to forge an agrarian utopia, resulting in the deaths of up to two million people from starvation, overwork and torture.