People look at the skulls of Khmer Rouge victims in this file photo. Photograph: DC-Cam

More than 30 years ago, the world mourned the deaths of the nearly two million people who lost their lives in Cambodia under the reign of the Khmer Rouge regime, which renamed the country Democratic Kampuchea.

The world acknowledged the State-sponsored torture, forced labour, starvation and executions that laid waste to Cambodia, marking one of the worst human tragedies in recorded history.

The overwhelming presence of mass graves and the loss of an estimated full quarter of the population of the country, told the story of what had transpired in stark numerical terms.

What remained untold, and what the world has not yet acknowledged, is the other calamity – that of widespread rape and other sexual crimes that took place under the Khmer Rouge, and were a central part of the range of atrocities perpetrated from January 1975 through to April 1979.

What was once silenced is now coming to light, as mounting evidence points to an array of sexual violence committed as part of the genocidal regime – including mass rape, gang rape before execution, rape as a form of torture, and sexual mutilation.

With the creation in 2004 of the Extraordinary Chambers in the Courts of Cambodia (ECCC), a Cambodian/United Nations hybrid tribunal established under Cambodian law to bring senior leaders and those most responsible for atrocities committed in Democratic Kampuchea to trial, victims of the full range of sexual violence committed under the Khmer Rouge had reason to believe that their experiences of violation would be among those considered by the Court.

Unfortunately, aside from the issue of forced marriage, crimes of sexual violence have only been marginally taken up by the ECCC, and experiences of sexual crimes have not been integrated into the court’s strategies, whether forensic, investigative, or prosecutorial.

In short, the court has determined that, though rape did occur, it cannot be linked to the accused and so is not included in the charges.

The court, which was created to give justice to survivors, is faced with a pool of victims without recourse to justice – and the accountability and acknowledgment it brings – for the crimes they experienced as part of the general atrocities.

Unless the court finds a way to address this issue, it will be perceived as implicitly re-enforcing the silence about conflict-related sexual violence, and not providing a counterbalance to the impunity that has prevailed.

Despite this, Cambodian women are beginning to speak up.

Over five months ago, in early December 2011, we were present at a Cambodian Women’s Hearing on Sexual Violence under the Khmer Rouge, when witnesses and survivors, as well as experts, came together to give testimonies about the vast numbers of rapes which were perpetrated by members of the Khmer Rouge against countless women, and the reign of impunity as perpetrators went unpunished.

The Hearing, which was convened in Phnom Penh by the Cambodian Defenders Project, gave survivors a public platform for the first time to demand justice.

We heard many stories, among them the devastating testimony of one woman, who, beginning from age 18, suffered multiple rapes and gang rapes, and instead of sympathy and care, faced mockery and prejudice from her community.

Distraught, she tried to commit suicide twice, and survived in dignity only by fleeing her village.

Another testifier at the hearing reported that she was among 30 women targeted for execution, with each woman methodically raped before being killed. She was the only victim who survived.

Experts asserted that the threat or experience of sexual violence was a daily reality for most women under the regime, that acts of sexual violence were seldom punished and implicitly endorsed by the “enemy policy” of the highest leadership, and that victim-survivors are still traumatized by the experience, and stigmatized by their communities.

After the Women’s Hearing I wrote to Prime Minister Hun Sen, and to the judges of the ECCC, to express my concern that survivors face obstacles in their quest for justice, whilst their perpetrators remain free.

I echoed the recommendations from the Women’s Hearing, that these crimes must be given the full benefit of the court’s resources and attention, as afforded other crimes against humanity before the ECCC, and I called for the establishment of mechanisms for appropriate recognition and reparations for victims of sexual violence under the Khmer Rouge regime.

It is imperative that these crimes do not remain “secret”, and it is critical that they are addressed formally and not stricken from the official historical record of the Khmer Rouge era.

Until the voices and experiences of women are part of this process, this chapter of Cambodia’s history cannot be considered closed.

The history of rape has been a history of denial, and it is unacceptable that it is the victim, and not the attacker, that is shamed and stigmatized.

The scope of what can be prosecuted must be revisited by the ECCC, and if prosecution is not possible, other alternative mechanisms to acknowledge these crimes must be established, utilizing the expertise of the court.

The government of Cambodia, which has an obligation to protect its citizens and to make an attempt to address ongoing injustices, must support survivors of sexual violence by addressing community stigma and lasting trauma and eliminating violence against women in present day Cambodia.

I call on the government of Cambodia and the ECCC to use their full and independent capacities to honour their courage and acknowledge the sacrifices of the victims and survivors.

Margot Wallström is the UN Special Representative of the Secretary-General on Sexual Violence in Conflict