An award-winning historian who has studied, and written extensively about, the Khmer Rouge regime was too busy to appear in person at the tribunal trying the alleged perpetrators of its mass atrocities, prosecutors told the court yesterday.

Prosecutors said author and Yale professor Ben Kiernan, who has studied Cambodia and the Khmer Rouge for about 40 years, was too busy to attend the UN-backed tribunal in person until some time in 2013.

“We request the chamber to allow his testimony by video link,” senior assistant prosecutor Vincent de Wilde said. “Video link or nothing are the only options before us.”

Defence counsel were incredulous at Kiernan’s inability – or unwillingness – to attend the tribunal in person and give evidence.

“We don’t see how it is that the gentleman is unavailable completely,” said Michael Karnavas, legal council for former foreign affairs minister Ieng Sary.

“He teaches a couple of classes [at Yale University] and the teaching schedule is already online, and he does not have any teaching obligations during the summer period,” Karnavas added. “The question is whether Kiernan is willing to come here, not whether he is able to come here.”

Kiernan first came to Cambodia to research the emerging communist party prior to 1975, before foreigners were evicted from Cambodia by the Khmer Rouge.

He subsequently returned to visit Thai refugee camps and spent the following decades conducting extensive research on the regime, collecting documents, writing books and articles on the events leading up to, during and after the fall of Democratic Kampuchea.

“We are disappointed by his apparent lack of enthusiasm to appear in court,” said Michiel Pestman, defence counsel for Brother No 2 Nuon Chea.

Defence counsel for former head of state Khieu Samphan likewise condemned Kiernan’s lack of availability “for an entire year”.

“I am somewhat puzzled by the apparent unavailability for an entire year of an individual  . . .  who has worked for more than 40 years on such a significant event as Cambodian history, and you are the international court designated to examine these facts and the individual does not find the time to attend these needs,” Anta Guisse said.

“His physical presence in the hearing is paramount.”

Both the prosecution and the civil parties maintained that hearing the expert by video link on a day yet to be determined would be sufficient.