The Khmer Rouge led by the notorious Pol Pot wiped out one quarter of Cambodia's population in the late 1970's.
100 million US dollars has been spent bringing Comrade Duch to trial and the court sentencing will be a huge and historic day for the many Cambodians and foreigners who still carry the scars of Pol Pot's regime.
Presenter: Conor Duffy
William Smith, prosecutor; Rob Hamill, brother of Khmer Rouge victim
CONOR DUFFY: In Cambodia's capital Phnom Penh is the extraordinary chambers in the courts of Cambodia. It'll be here under a giant Cambodian flag where Kaing Guek Eav, better known as Comrade Duch, will meet his fate.
He's confessed to being personally responsible for the deaths and torture of more than 12,000 people. Australian lawyer William Smith has been one of the lead prosecutors in the case.
WILLIAM SMITH: Today will be a historic day in Cambodia particularly for the court but particularly for the Cambodian people. It is the first time that a court has ever held anyone to account for the crimes committed during the Khmer Rouge period. Many, many victims have had their voices muzzled for 30 years.
CONOR DUFFY: William Smith will be one of the few people allowed through the bullet-proof glass to see Comrade Duch sentenced face to face. He says that even after all these years it's important that justice be done.
WILLIAM SMITH: I've seen Duch before during the trial. He believed in what he did during the period. He has come to the court and said that he apologises to the victims for what has happened.
It will be, in a sense, another day in court but really I don't think it is a day that is as important for the accused as it is for the Cambodian people, the victims that suffered.
CONOR DUFFY: A man who'll be on the other side of the glass keenly awaiting the sentencing is former New Zealand Olympian Rob Hamill.
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AM caught up with him with him at a busy Phnom Penh restaurant where he was discussing the case. Rob Hamill's brother Kerry Hamill was captured by the Khmer Rouge in the late 1970s, while on the trip of a lifetime sailing around the world.
He was tortured at the S-21 prison by its chief Comrade Duch before being sent to the killing fields and Rob Hamill is concerned Duch will get less than the prison sentence requested by the prosecutor, William Smith.
ROB HAMILL: Forty years has been asked for from the prosecution although the prosecution says they have considered the mitigating circumstances but I suspect the court will mitigate on that 40 years and could bring it down lower.
CONOR DUFFY: Rob Hamill and his family still don't know where Kerry Hamill is buried and Mr Hamill is pushing for a private meeting with Comrade Duch to learn exactly what happened to his brother.
ROB HAMILL: I just really want to know. Ultimately where he is, where he lays.
CONOR DUFFY: Many Cambodians will be bussed in to the court from the provinces today to see this historic sentencing for themselves, and just like Rob Hamill, they'd like answers on what happened to their loved ones.