One of the leaders of the former Khmer Rouge regime will be set free after a court in Cambodia ruled Thursday that she was medically unfit to stand trial for genocide, a decision survivors called shocking and unjust.

Cambodia's U.N.-backed tribunal issued a statement saying that 80-year-old Ieng Thirith suffers from a progressive, degenerative illness that is likely Alzheimer's disease and which diminishes her mental capacity.

"There is no prospect that the accused can be tried in the foreseeable future," the tribunal said. "Experts have confirmed that all treatment options have now been exhausted and that the accused's cognitive impairment is likely irreversible."

She is "unfit to stand trial," the statement said. Thursday's decision upheld an earlier ruling that was put on hold pending the opinion of medical experts.

A tribunal spokesman, Neth Pheaktra, said Ieng Thirith would be freed Friday from the tribunal's detention facility if prosecutors do not appeal.

Ieng Thirith was the Khmer Rouge's minister for social affairs and the regime's most senior-ranking woman. She also was the sister-in-law of late Khmer Rouge leader Pol Pot. She is accused of involvement in the "planning, direction, coordination and ordering of widespread purges," and was charged with crimes against humanity, genocide, homicide, torture and religious persecution.

Ieng Thirith has said that the charges against her are "100 percent false" and that she always worked for the benefit of the people.

The U.N.-backed tribunal is seeking justice for an estimated 1.7 million people who died of starvation, exhaustion, lack of medical care or execution during the communist Khmer Rouge's 1975-79 rule.

Three other senior leaders are currently on trial, including Ieng Thirith's husband, 86-year-old Ieng Sary, the regime's former foreign minister. Also on trial are 85-year-old Nuon Chea, the Khmer Rouge's chief ideologist and No. 2 leader behind the late Pol Pot, and 80-year-old Khieu Samphan, a former head of state.

The tribunal's statement stressed that Ieng Thirith's release did not mean the charges against her were being withdrawn and that it was not a finding of guilt or innocence. It plans to consult annually with experts to see whether future medical advances could render her fit for trial. In the meantime, she cannot leave the country or have contact with other defendants, with the exception of her husband, the statement said.

Survivors of the Khmer Rouge era were stunned, including 71-year-old Bou Meng, whose wife and two children were executed at the notorious S-21 prison in Phnom Penh.

"I am shocked," Bou Meng said. "I had always hoped that the Khmer Rouge leaders would be brought to court for justice — but now they are freeing her."

He called it "a mockery to the deaths of so many Cambodian people," and asked, "Where is the justice for my dead wife and children?"

Others said the development highlighted one of the main complaints against the tribunal — that it is too late to truly deliver justice. Pol Pot, the regime's top leader, died in 1998.

The tribunal opened in 2006 — nearly three decades after the fall of the Khmer Rouge — following years of wrangling between Cambodia and the United Nations. The lengthy delays have been costly and raised fears that the frail surviving Khmer Rouge leaders will die before their verdicts come.

"Of course if she is seriously ill with Alzheimer's, she should be released. There is no point in trying an incapacitated person," said Theary Seng, a human rights advocate representing some victims who are allowed a role in the proceedings. "The point is the (tribunal) is so late in coming. The political foot-dragging and inertia has caused this travesty of justice."


Associated Press writer Jocelyn Gecker in Bangkok contributed to this report.