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PHNOM PENH - Cambodia's Appeal Court today upheld the conviction of former Wellington traffic officer Graham Cleghorn, a decision that leaves him locked in Phnom Penh's Prey Sar prison until 2024 for raping five teenagers.

Cleghorn, 60, was not present at the court today in Phnom Penh, but one of his defence lawyers, Ouk Ry, called the verdict unfair and said his client would appeal to the Supreme Court.

Another of Cleghorn's lawyers, Nou Tepirith, claimed that the prosecution lacked the forensic evidence needed to keep Cleghorn in prison for his 20-year sentence.

"Rape cases need material evidence gathered by science and technology, not just verbal testimony," he told reporters.

"They should not just believe in a few girls who were bribed, they should base their verdict on scientific research."

But Nou Navy, the victims' lawyer, said enough "parallel evidence" was presented to uphold the sentence.

"Even though our country does not have materials to take sperm and do a clear diagnosis, we have some parallel evidences," she said.

"First, we have victims' testimony. Second, we have witnesses' testimony -- two physicians. Also the perpetrator's wife admitted that she took girls to be injected (for contraception). And furthermore, the other girls saw the perpetrator take the girls into the room and then turn off the light."

Grant Traill, counsel at the New Zealand Embassy in Bangkok, attended the court but declined to comment on the proceedings.

"New Zealand does not hold any opinions on the outcomes of criminal proceedings against New Zealanders. We only require that due process is followed," Mr Traill said.

"As long as the appeal process was in accordance with Cambodian law and proper judicial process the verdict must be accepted."

Cleghorn, who moved to Cambodia in the late 1980s and was briefly a monk, has worked as a tourist guide and bar owner in Siem Reap.

He was sentenced by Siem Reap Provincial Court to 20 years' jail for the rape of five girls aged between 14 and 19 at the time off the offences in 2003, and for possessing an illegal firearm.

His Cambodian wife, Bout Toeur, was convicted of conspiring to collude in the rapes, providing the girls with regular contraceptive injections under the guise of "beauty shots".

She received a three-year suspended sentence.

But Cleghorn has maintained his innocence and claimed that judges, police and the staff of a women's organisation engineered false accusations against him.

In 2006, Oong Chantol, director of the Cambodian Women's Crisis Centre, said she feared Cambodia's Appeal Court would overturn the charges following New Zealand's diplomatic intervention in the case in March -- which she called "unnecessary".