A UN-backed tribunal in the Cambodian capital of Phnom Penh is holding its first initial hearing in the trial of four former top Khmer Rouge leaders.
The defendants include the No. 2 in Pol Pot's regime, Nuon Chea.
His defense lawyer, Michael Pestman, argued that the investigation into the case had lacked transparency and suffered from government interference.
"We have raised several preliminary objections," Pestman said. "And most importantly, our main objection was against the judicial investigation carried out by the investigating judges that was so unfair and so harmful to the rights of our client, Nuon Chea, that we think that we are of the opinion -- and so is our client -- that these proceedings should be terminated."
The four defendants face charges of genocide and crimes against humanity over the deaths of an estimated 1.7 million Cambodians from 1975 to 1979.
They were among the inner circle of the late Pol Pot, the architect of the Khmer Rouge's ultra-Maoist revolution. They all deny the accusations.
The trial proper is expected to start in September and is likely to last for years.
compiled from agency reports