Transatlantic rower Rob Hamill will head to Cambodia shortly, clinging to the hope of a private audience with the Khmer Rouge henchman who headed the prison where his older brother Kerry was tortured and killed.

Mr Hamill will be at the United Nations-assisted Extraordinary Chamber of the Courts of Cambodia (ECCC) at Phnom Penh for the July 26 sentencing of Kaing Guek Eav, known as "Duch", the former head of the S-21 or Tuol Sleng prison.

Mr Hamill's older brother Kerry was imprisoned at S-21 when the yacht he and friends were sailing to Bangkok strayed into Cambodian waters on August 13, 1978.

Canadian crewman Stuart Glass was shot dead while Mr Hamill and Briton John Dewhirst were accused of being CIA spies and taken for interrogation.

In January 1980, the Hamill family learned Kerry had been tortured for two months before he signed a "confession" and was murdered.

Rob Hamill, who was 14 years old when he saw his brother Kerry for the last time, yesterday told the Herald that he was hopeful of a private audience with Duch after his sentencing, having made the request through his lawyers to Duch's legal counsel about a month ago.

"In his final statement during the trial he said he would see any of the family members if they wanted to speak with him, so I would be disappointed if he said no," said Mr Hamill.

"I've had my say in court and told him what I think so I don't need to go there. What I need to try and get is some sort of understanding of what he was thinking at the time. He probably had some genuine causes which he felt would be best for Cambodia at the time so my mission would be to try and understand where that changed."

Mr Hamill said the prosecution had sought a 40-year imprisonment term for Duch, who oversaw the torture and executions at the prison of about 16,000 men, women and children.

Cambodia does not have the death sentence, which is something the Hamiltonian said he would not have endorsed for the 67-year-old.

Duch has already served 12 years in jail, something Mr Hamill sees as problematic.

"If he got a 20-year sentence he'd be out in eight but I think for the rest of his living days inside a prison would be a fair outcome for everyone, all the people I have spoken to in Cambodia think he should be locked away for life, even the kids. There's an understanding that he has to pay for what he did and his role in effectively overseeing the deaths of all of these people."

Asked if the sentencing would provide some closure for him, his family and friends, Mr Hamill said: "It's a continuation of several processes. It's been 32 years since Kerry went missing and I see this as kind of a milestone in the continuing process for getting some justice but also for reconciling all those deaths.

"My mother never got to see this sort of justice done which is sad. We have a desire to see justice done but there's also the grieving process."

Led by Pol Pot, who died in 1998, the Khmer Rouge sought to set up a communist utopia.

Up to two million people died from starvation, overwork, torture or execution during the 1975-1979 regime.