The Khmer Rouge tribunal on Monday heard testimony from an official of the Documentation Center of Cambodia, who said the hundreds of thousands of documents submitted to the UN-backed court have been carefully scrutinized for authenticity.

Vann Than Peou Dara, deputy director of the center, was summoned after defense attorneys for Khmer Rouge leaders on trial expressed doubt over the documentation.

Documents are carefully examined and verified by their sources before they are admitted to the court, he told the court.

Defense attorneys subsequently said their doubts would not be allayed by the deputy, and they called for the appearance of the head of the center, Chhang Youk.

The Documentation Center has collected nearly 1 million documents on the Khmer Rouge since it began as a field office for Yale University genocide researchers in 1995.

Nearly half a million documents have been handed over to the courts, Vann Than Peou Dara said Monday.

Many of those documents were preserved by Vietnamese forces after the ouster of the Khmer Rouge in 1979, he said.

Monday’s hearing coincided with the arrival of the UN’s new special expert for the tribunal, David Sheffer, who is expected to address an ongoing controversy in the court’s office of investigating judges.

The UN-appointed judge Siegfried Blunk resigned last year, citing political interference in two cases before the court, and the Cambodian government has so far refused to approve the nomination of his replacement, Laurent Kasper-Ansermet.

Scheffer met with tribunal officials on Monday and is expected to meet Cabinet Minister Sok An, who is in charge of the tribunal for the government, as well.