Khmer Rouge guerrillas pose for a photograph following the fall of Phnom Penh in 1975. Tribunal documents outline a war with Vietnam that began as soon as the guerrillas took power.

The executions of ethnic Vietnamese by the Khmer Rouge could be the key to genocide charges for jailed leaders of the regime, but prosecutors documents also recount a conflict between the Khmer guerrillas and their Vietnamese neighbors that began almost immediately after the Khmer Rouge came to power.

The Vietnam government does not fund the Khmer Rouge tribunal, but more Vietnamese nationals were killed by the regime than any other foreign group. The regime also killed Thai, Lao, French, New   Zealand and US nationals.

"Regarding this issue, several powerful countries, rich countries, have assisted in funding the Khmer Rouge tribunal already," Vietnamese Embassy spokesman Trinh Bac Cam said Wednesday.

Closing orders in the case of Kaing Kek Iev, also called Duch, issued by tribunal judges claim at least 400 Vietnamese civilians and soldiers were killed at Tuol Sleng prison alone.

Youk Chhang, director of the Documentation Center of Cambodia, said at least 600 Vietnamese were killed by the Khmer Rouge at Tuol Sleng and another detention center in Prey Veng province.

In highlighting the conflict, which led to the eventual invasion of Cambodia by Vietnamese forces and the ouster of the Khmer Rouge, tribunal documents are fulfilling a quieter role of the tribunal: a recounting of history that has been lost on Cambodians in subsequent years.

According to indictment documents posted by tribunal prosecutors recently, the Khmer Rouge maintained a conflict with Vietnam over border disputes between April 1975 and December 1978.

The conflict took place in border areas including Ratanakkiri, Mondolkiri, Takeo, Svay Rieng, Kampong Cham and Prey Veng provinces, and on the island formerly known as Koh Tral, better known now by its Vietnamese name, Phu Quoc.

An invasion force of 150,000 Vietnamese troops began an offensive in December 1978, driving the Khmer Rouge out of the capital on Jan. 7, 1979.

The conflict, and suspicions of Vietnamese agents withing the ranks of the Khmer Rouge, led to the killing of many Vietnamese.

"If there will be a trial, justice is for all victims," Trinh Bac Cam said.

Tribunal observers said recently prosecutors could seek genocide charges against the five jailed Khmer Rogue leaders for the killing of the Vietnamese.

"A part of justice will be shared with Vietnamese citizens who have their relatives, military and civilian, killed during Democratic Kampuchea," Youk Chhang said.