By Prak Chan Thul
PHNOM PENH (Reuters) - One of the most senior figures in Cambodia's brutal Khmer Rouge regime is set to walk free this week after an international court ruled on Thursday she was mentally unfit to stand trial.
Ieng Thirith, a former social affairs minister and sister-in-law of the late architect of the 1970s "Killing Fields" revolution, Pol Pot, had made no improvement in her mental state since last November, the court said, when experts said she was suffering from Alzheimer's disease.
The 80-year-old, known as the "Khmer Rouge First Lady", would be released on Friday if no appeal was lodged by prosecutors, said Neth Pheaktra, a spokesman at the Extraordinary Chambers in the Court of Cambodia (ECCC), as the hybrid United Nations-Cambodian tribunal is known.
Although a recovery was never expected, the release of Ieng Thirith, a French-educated former Shakespeare scholar, will be another blow for Cambodians seeking an explanation for the horrors of the Khmer Rouge's four-year reign of terror.
Since it was set up in 2005, the court has suffered from a shortage of funds and has been beset by resignations and allegations of political interference. It has delivered only one verdict, life imprisonment for the chief of the notorious Tuol Sleng Prison, Kaing Guek Eav, better known as Duch.
An estimated 1.7 to 2.2 million people - nearly a quarter of the population - died during Khmer Rouge rule from 1975 to 1979. They were executed or tortured to death or died of starvation or disease during Pol Pot's attempt to create a peasant utopia.
The ECCC said in a statement there was no chance Ieng Thirith could be tried in the foreseeable future, so the charges of crimes against humanity and genocide would be dropped and the court was "obliged to order the accused released from detention".
Ieng Thirith was one of four elderly and frail defendants in case 002, the court's most high profile case to date.
Others in the dock are "Brother Number Two" Nuon Chea, ex-president Khieu Samphan and former foreign minister Ieng Sary, Ieng Thirith's husband.
Many Cambodians fear that because of the complexity of their cases, the elderly suspects could die before a verdict is delivered. Ieng Sary, 87, is in hospital suffering from dizziness and fatigue.
Stephen Rapp, U.S. ambassador at large for global criminal justice, told reporters the ruling was a "well founded decision" based on evidence and expert opinion. The United States announced on Thursday it would give another $5 million to the tribunal to help with funding.
Ieng Thirith was the sister of Pol Pot's first wife, Khieu Ponnary. She died in 2003.
(Editing by Martin Petty and Robert Birsel)