Neary Adeline Hay’s decision to study art in university was an act of defiance against her parents. Nothing new there, it seems – but unlike her more privileged peers, her choice was driven by something more profound than merely juvenile rebellion.

It was how she vented her frustration at being kept in the dark throughout her adolescence in France about what her family went through in Cambodia during the Khmer Rouge era. “When I lived with my family, it was like living in Cambodia – but that of their youth. My parents were just frozen in the 1970s,” she said about growing up in Paris, where her family settled down in 1984 after fleeing Cambodia three years previously.

“At home it was very traditional . . . My parents were very strict with me, they always told me, ‘You’re not French, you’re Cambodian.’ But how can I be Cambodian when I don’t know anything about Cambodia, when they never talked to me about anything? I was so revolted – this anger made me [choose] artistic studies, as it was the only way I could express these questions.”

Back then, Hay likely couldn’t imagine that her art would actually generate some answers to these questions and also a reconciliation between herself and her stoic parents. That long process would eventually culminate in a documentary tracking her father’s return to Cambodia and his meetings with some of the very people who laid his life to waste nearly four decades ago.

Premiering at the International Film Festival Rotterdam last week, Angkar follows Khonsaly Hay as he travels around Phnom Penh seeking what remains of the house and pharmacy he was forced to leave behind during the Khmer Rouge-instigated mass exodus from the city on April 17, 1975.

He then visits the village in Preah Vihear province where he was assigned to live after a failed attempt to flee the country. The film’s title, which means “organisation” in Khmer, is a nod to the name by which the Khmer Rouge referred to their regime.

It is her first feature length film after two shorts, Il était une fois notre enfance (2005) and Des maux à mots dire (2010).

In what is probably the documentary’s most heart-wrenching scene, he meets four of his former tormentors who insist on downplaying their roles and misdeeds – with one of them actually claiming to have “no blood on my hands” while saying that his prisoners had been better fed back then than he and his fellow guards.

A still from the documentary film Angkar, showing Khonsaly Hay in the village in Preah Vihear where he was taken by the Khmer Rouge. Rotterdam International Film Festival

A revealing document about the unreconciled trauma haunting Cambodians today, Angkar is also a personal and poetic piece in the shape of a conversation between the 36-year-old filmmaker and her father. The film is defined by their voiceovers: Hay Sr’s painful recollections delivered in Khmer and Hay’s French-language response to her father’s views.

Hay, who was only 3 months old when her parents fled with her to Thailand, said she has wanted to have this conversation since she was little. But her parents – and much of the diaspora in Paris – have seemingly agreed to a pact of silence about what they went through under the Khmer Rouge.

She didn’t insist, knowing at least of the hardship her parents went through after their escape from Cambodia. The family spent nearly three years in Thailand and Indonesia before arriving in France.

“We were so poor,” she said. “My father was a pharmacist, but when they arrived in France they had nothing. Their diplomas were not recognised, and my father washed plates in restaurants for a living.”

She was still unaware of her parents’ life stories when she went to Cambodia for the first time in 2001 when she was in university. “I raised €5,000 ($6,200) to create a project with an NGO to help children,” she said. “I was so guilty of having a chance to grow up in a country like France, and I wanted to give something back to the kids – at the time I was very young and also very naive.”

She recalled telling her parents about her experiences, only to find them perplexed about the whole thing. More importantly, her parents refused to accompany her back to Cambodia, resistant to facing their past.

Hay said her father finally relented a decade ago, resulting in an outpouring akin to a “vomiting” of pent-up angst, in which he recounted the horrific departure from Phnom Penh, his suffering in the Khmer Rouge detention camps, and the death of his whole family.

“I was surprised to discover this man, my father, had another life before me,” she said. “He would talk about his nephews, his sisters, how they would go to the cinema every week [before 1975] and all the realities of those days,” she said. “When he started to talk about the past, it seemed to me I had in front of me a kind of puzzle, the identity of a man I thought I knew but I didn’t know at all.”

Her father’s revelations also unleashed her own identity crisis, as she discovered her parents had been brought together in a forced marriage in their prison camp. “Angkar created me, in a way,” she said.

In turn, Hay decided to create an Angkar of her own. “When he started to tell me about his story, I thought I had to make a movie about this, because this generation is going to disappear in 10 or 20 years,” she said. “The real people who lived through this are starting to talk about this, and he also showed me things which are testament to this.”

Hay said she has been in constant touch with Rithy Panh, the celebrated Cambodian filmmaker, who she met in 2001 after sending him a poem about her first trip to Cambodia. “At that time I followed [his work] because there was only him,” she said. “Sometimes I consulted him about my projects. I met him many times and at one time there was the discussion of him working with me on the film also.”

As Angkar begins its trek on the festival circuit after its world premiere in Rotterdam, Hay has already begun writing her next film. The story will revolve around a road trip across Cambodia undertaken by a French-Cambodian man, a young local boy and hundreds of ducks. “I’m trying to show the complexity of [the country’s] society – by using humour to show a vision I have of Cambodia,” she said.

But the pressing issue at the moment is getting the French-funded Angkar shown in Cambodia – and also to her parents.

“My mother couldn’t take it at the moment,” Hay said. “And my father saw it three days [before the world premiere] for the very first time – he saw nothing at all before, not even the rushes. And he cried . . . he asked how I could describe it so well what he felt. And to me that’s the best possible gift.”