A few years ago, I find myself travelling through South-East Asia, at one point trying to piece together a baffling series of events that resulted in the genocide of a third of Kampuchea, or Cambodia as we now call it.<br /><br />I read as much as I can, and try to speak to survivors. But the eyes of family members well up with tears. The inexpressible grief is barely contained. Out of respect, I desist.<br /><br />Some time later, I see this film by internationally acclaimed human rights director, Rithy Panh. He has a better reason for asking  he survived the massacre. His work, unlike my simple desire for knowledge, would provide momentum for confessions and now a war crimes tribunal. At the 'Killing Fields' outside Phnom Penh is a tree against which children had their brains bashed out. In the film, a guard explains how parents would be separated from each other, and from their children, to minimise fuss. The adults were told not to worry: they were going to a new home. They were then blindfolded for 'security reasons' and, ammunition being scarce, hit on the back of the neck with metal bars before being cast into a pit.<br /><br />Executions followed three levels of torture at S.21, a school building in Phnom Penh converted into a concentration camp (and now a memorial visitors centre). Details are so hideous  humans packed like abattoir carcasses, and systematic torture, that you could be forgiven for suspecting truth has been embroidered. Except for one fact. Meticulous records of every victim were kept. Each non-person, each beating, each flaying of skin, each removal of fingernails, chemical and electrical abuses, rape. Precise details of prisoners chained to iron bars to sleep, crammed together top-to-toe, living sharing a sardine-row with the dead.<br /><br />Rithy Panh's master stroke brings together S.21 survivors (two of the existing three) and former guards and torturers. He encourages them to talk. To find answers. One of the hardest things, even now, is these perpetrators see themselves also as victims. They joined Pol Pot's Khmer Rouge for what seemed like all the right reasons. Once inducted, they were brainwashed, indoctrinated and trapped. Deviation meant the same fate as those they flayed alive. Most were youths at the time, easily manipulated. But, how can you forgive and move on, when no-one will admit wrong-doing? Even Pol Pot blamed the people he left in charge.<br /><br />Men joined the Khmer Rouge because their villages were being repeatedly bombed. With their government's approval. The much loved Prince Sihanouk had been ousted in a coup. Lon Nol, an ineffective, U.S.-backed ruler, was forcibly installed in his place. Lon Nol gave America (under Johnson and Nixon) 'permission' for what became the largest bombing campaign in human history. Two and three-quarter million tons of bombs  the revised figure released by the Clinton administration  was more than the total dropped by all the allies in the whole of World War Two (which only came to two million, even including Hiroshima and Nagasaki). Whole areas of the country became pock-marked, aerial chemical deforestation destroyed livelihoods and created famine and disease. Thousands killed, many more permanently displaced. The Khmer Rouge leaders kept their extreme agenda  a form of rural, back-to-basics communism  completely secret until they were installed in power. Then the purges started. Lon Nol supporters were followed to the grave by academics or anyone tainted with 'western' ideas. Anyone opposing Pol Pot, or whose name was elicited under extreme torture. The population was turned out of the cities, dying of starvation. With no-one else to purge, the despots found traitors to execute its own members.<br /><br />Kampuchea's leading doctor, Swiss born Beat Richner, adamantly told me that without American intervention  which had been aimed ironically at stopping communism in the region  there would have been no Khmer Rouge. No Pol Pot victory. Richner worked in Kampuchea before, during and after Pol Pot, and his coal-face assessment agrees with most historians. But it is controversial: the U.S. military claim that Pol Pot would have won anyway. Ordinary Cambodians are still grieving rather than blaming. Rithy Panh's film exposes horror without finger-pointing. There are no 'lessons to be learnt.' Millions died  estimates say around a third of the population, two to three million. (And this in a country smaller than Great Britain. As a benchmark comparison, Hitler exterminated six million Jews .) While Panh documents the existence of atrocities, he does little to substantiate the bigger picture, which has to be gleaned elsewhere or from casual remarks of the former guards.<br /><br />Rithy Panh's film, S.21  The Khmer Rouge Killing Machine, has no real ax to grind  in the tradition of best documentary, it simply tries to provide a window. While it is powerful evidence, many viewers might find it emotionally less satisfying than more box-office friendly film by Roland Joffé, The Killing Fields, which (symbolically) suggests the West's responsibility by the journalist who 'uses' his Cambodian friend for his own ends, and also has more of a story. Either way, it is a country that makes me ashamed to be a Westerner. Yet Cambodians have more to worry about than my sense of emotional well-being. Avoiding hunger, or the thousands of landmines that still litter their country. In Joffe's film, an American journalist travels to a Red Cross camp to be reunited with a Cambodian colleague he deserted to his fate. "Do you forgive me?" he asks. The Cambodian answers with a smile, "Nothing to forgive, Sydney, nothing to forgive." Although it won many awards, Panh's movie is rarely shown outside of Cambodia. There you can pick it up for about $3. From one of the many maimed or desperate hawkers that haunt the road outside Tuol Sleng Genocide Museum. This place formerly known as Security Prison 21, or 'S.21' for short, still has living ghosts. The film just tells us where they came from.