VENICE - Joshua Oppenheimer's "The Act Of Killing" was an incredibly uncomfortable watch for many reasons. Not least its close alignment - narratively, if not morally - with Indonesian death squad veterans, as they re-enacted the atrocities they had committed in the style of their favorite films. "The Look Of Silence", styled as a companion piece rather than a sequel, redresses the balance. This time, the surviving family members of Ramli, one of the the victims, are the focus, and the style is appropriately restrained.

We open on a man wearing an optician's glasses. He gazes unflinchingly through the apparatus at the camera. The documentary that follows will be an exercise in continual small adjustments of perspective with the aim of finding the clearest possible window on the horrifying recent history explored more theatrically in "The Act Of Killing". In the next scene, we watch a former member of a death squad recall his crimes, but we're not the only ones watching him. This time, we're looking at things from the viewpoint of the victims.

44 year old optician Adi is both the film's central subject and, in a sense, our host. It is Adi who views footage of men boasting of having committed murder. It is Adi who subsequently asks the questions and guides the interviews that follow. It is Adi whose brother Ramli was killed before he was born, and Adi's mother who describes him as the answer to prayers that she would have another son like Ramli. Two years after Ramli's death, Adi was born.

We are introduced to Adi's mother as she washes her aged husband (he claims to be 16 or 17 years old; his ID suggests he was born in 1909) while recounting how her first son was maimed, murdered and dumped in a river. Oppenheimer makes it clear from the outset that this time we're in the world of victims' testimonies and not those of the perpetrators - we will hear from the killers too, but in the context of this film they are here so that we can experience Adi's remarkably calm response to their murderous braggadocio.

It's probable that some will accuse this doc of manipulation or tastelessness, or of being too keen to observe the face of a human being taking in the firsthand testimony of someone who killed their relative. I didn't ultimately find "The Look Of Silence" to be either tasteless or manipulative (Grim? Yes. Difficult? Yes. Manipulative? No.) That's partly because of Oppenheimer's rigorous control of his material, and partly because he and his team have located in Adi such a strong, sensitive and intelligent individual.

Adi is incredibly polite to the last people in the world he owes anything to: "I don't mean to offend you, but I think you're trying to avoid moral responsibility." At one point, one of the murderers even complains "you ask much deeper questions than Joshua ever asked. I don't like it." In offering Adi the chance to shape his own story and directly question those responsible for his brother's death, Oppenheimer adds a much needed extra dimension to the collective effort to tell the story of this shameful period in history. Not everyone is so moderate: Adi and Ramli's mother prays that the murderers' children and their children's children will suffer.

In one particularly uncomfortable section Adi civilly asks what would have happened to him during the military dictatorship. His interviewee, a death squad commander, is discomfited but determined to emerge triumphant from the exchange. "You can't imagine..." he smiles, "so continue with this communist activity." It's a veiled threat, delivered with a smile, but his eyes aren't smiling. Understandably, Adi's mother is worried - "Be very careful. They'll send thugs to rip you apart" - and it's an anxiety viewers will share. The dozens of anonymous credits when the film ends are testament to the very real danger posed by plenty of the film's subjects.

Details of individual killings are predictably grim, but I personally felt they were editorially justified. Although this is a companion piece to "The Act Of Killing", it is not a sequel and needs to be able to stand alone; without some sense of the atrocities committed, it would be difficult for the filmmakers to realize that aim. Aspects of what happened are therefore worth reinforcing, however uncomfortable it might make us to hear about them: this was not a clinical process (and obviously this is not to suggest that the horror would have been in any way ameliorated if it had been). The fact is that these murders were grotesque and bizarrely ritualized with various superstitions attached.

As more than one death squad member recalls: "Luckily, I drank blood. If not, I'd be crazy." It's all the more disgusting to remember that so many of these men are still in power, including a head of the legislature who cautions the filmmakers: "If you keep making an issue of the past, it will definitely happen again."

The film is rightly preoccupied with the mistakes of the past, the relevance of history and the lessons history can teach - or rather can't teach if that history is bastardized. A classroom scene shows a state-sanctioned version of these events being taught to schoolchildren. It bears about as much relation to what really happened as the schoolbooks of Oceania do in George Orwell's 1984.

Given this emphasis on establishing fact, a relevant area that feels perhaps marginally under served is US historical complicity with the mass killings (the American Embassy in Jakarta supplied the Indonesian military with lists of up to 5,000 suspected Communists). The hundreds of thousands of murders took place in an era when American politicians were terrified of communists, and Oppenheimer finds room for chilling NBC footage from Ted Yates reporting the events as "the single biggest defeat" of communists where "in many cases, whole families were liquified." Later, an interview with a commander responsible for ordering the murders of 500-600 people proposes that he and his colleagues should be rewarded with gifts for their actions "because this is an international issue" and "America taught us to hate communists", although of course the extent to which his testimony can be taken at face value is limited.

A laser-focused testimony of great value (and probable recognition come awards season, especially since "The Act Of Killing" lost out to "20 Feet From Stardom" at the Academy Awards), "The Look Of Silence" represents a tough but essential counterpoint to the more obviously extraordinary first film.