Olympic rower Rob Hamill says it is a huge relief that the man who admitted to overseeing the torture and killing of his brother as the Khmer Rouge's chief prison warden, has had his appeal rejected and his sentence increased to life imprisonment.

The prison chief responsible for the torture of New Zealander Kerry Hamill, who was later killed by the Khmer Rouge regime, has had his sentence increased to life in prison.

Hamill, Canadian Stuart Glass and Englishman John Dewhirst were on the yacht Foxy Lady when it went off course, possibly due to a storm, and came to a small island in Cambodian waters. The men took shelter there, but were discovered and later killed by the Khmer Rouge in 1978.

Cambodia's UN-backed genocide court today rejected the appeal by Khmer Rouge jailer Kaing Guek Eav "Duch", who was jailed in 2010 for his role in running a notorious prison where thousands of inmates were killed.

"The penalty must be harsh to prevent similar crimes, undoubtedly among the worst in human history," the president of the court chamber, Kong Srim, said in reading the verdict.

He described Duch as a "shocking and heinous character" who had overseen a "factory of death".

Duch, 69, confessed to the torture of more than 12,000 people - among them Rob Hamill's brother, Kerry - before they were executed during his tenure as chief of the notorious S-21 prison in Phnom Penh, Cambodia's capital.

Duch's guilty verdicts on murder, torture, rape and crimes against humanity in July 2010 in the court's only ruling to date. He was given a 35-year jail term but that was immediately commuted to 19 years because of time already served in military detention.

Duch appealed against the decision, arguing that the court had no jurisdiction to try him because he was not a top commander of Pol Pot's ultra-Maoist regime, under which an estimated 1.7-2.2 million people died.

The prosecutors and civil parties also appealed, demanding a heavier sentence.

Duch's defence lawyers claimed he was not the most responsible senior official at S-21. and was merely a junior official following orders.

But judges rejected his claim and increased his sentence from 35 years to life.

Mr Hamill said he was hoping to see Duch put away "for the rest of his living days" as no number of years could serve as justice for his brother's death.

"I didn't dare believe that he would get a life sentence. It was just too much to kind of hope for," Mr Hamill  said.

"It's huge. The more I think about it it's very significant."

He said there was no rush of emotion on watching the verdict announced live online, but it was a weight off his shoulders.

"This has just been such a long process. I have to say I've built up a bit of a thick skin through it all now.

"It's just a relief."

The tribunal has separately put the three most senior surviving leaders of the Khmer Rouge regime on trial. Pol Pot, the architect of the agrarian revolution, died in 1998.

- With Reuters

- © Fairfax NZ News