PHNOM PENH, Cambodia (AP) — Cambodia plans to renovate the skull-filled memorial on the site of the Khmer Rouge's former "killing fields" for the first time since it was built two decades ago.

Now a grim tourist attraction, Choeung Ek outside the capital Phnom Penh was where most of the prisoners who were tortured at the regime's main prison, S-21, were taken to be killed.

The remains of some 8,900 human skulls and bones are displayed in glass cases inside a Buddhist stupa-style structure, a religious monument, that was built in 1988 and has never been renovated, said Chour Sokty, the site's director.

He said experts will begin cleaning the stupa's roof, repainting the structure's white facade, cleaning an accumulation of cobwebs and repaving the area outside the building.

"We will be painting and cleaning its roof and the grounds. We will not move any of the skulls and bones inside the stupa," Chour Sokty said. "We want to beautify the stupa so it stays strong forever."

The Khmer Rouge were responsible for killing an estimated 1.7 million people during their 1975-79 rule.

A U.N.-backed tribunal last month convicted the regime's chief jailer, Kaing Guek Eav — also known as Duch — of war crimes and crimes against humanity, in the first verdict against a major Khmer Rouge figure 30 years after the regime's downfall.

Duch was ordered to serve 19 years in prison, a sentence that has been criticized in Cambodia as insufficient given the magnitude of his crimes.

Four other former senior leaders of the regime are in custody awaiting trial.