In his testimony to the Khmer Rouge tribunal, celebrated artist Vann Nath described the scene that provoked him to craft a painting that now hangs at S-21.

It shows a man being suspended from a wooden frame “where children used to play”, his hands tied behind his back, as another man, his hands also bound, is plunged head-first into a large jar of water.

These victims, along with thousands of others, met their fate after confessing under torture.

This image remains a constant reminder of the anonymity of so many victims of torture whose suffering remains largely unknown and undocumented.

Today is the International Day in Support of Victims of Torture, an occasion to remember victims and highlight the unambiguous, absolute prohibition on torture and all forms of cruel, inhuman and degrading treatment or punishment.

It is also the 25th anniversary of the UN Convention Against Torture.

It is worth remembering that torture is defined under international law as the intentional infliction of severe physical or mental pain or suffering, by or on behalf of the authorities, on a person for the purpose of obtaining information, or of punishing, intimidating, or coercing that person or another person.

The prohibition of torture remains a fundamental pillar in the protection and promotion of human rights.

Limits can be placed on the exercise of some human rights, but protection from torture is not one of them. Like slavery and genocide, its prohibition is absolute.

Orders from a superior are no excuse for committing torture.

Sending a person to another country where there is a risk of torture is unacceptable. This reflects the abhorrence with which the international community views the crime of torture.

No country can be complacent about torture. By its very nature, torture takes place behind closed doors, away from scrutiny: in prisons and police stations, but also in immigration detention centres, mental hospitals or drug treatment centres.

People detained in these places are at risk of many human-rights violations, but torture and deprivation of the right to life are the most serious.

For this reason, specific safeguards need to be in place. Law-enforcement personnel must be educated about the prohibition on torture and how to recognise when it occurs.

Places of detention must be regularly and independently monitored to reduce the risk of torture.

Complaints – or even reasonable suspicion – of torture must be promptly and impartially investigated, and a system put in place to protect complainants from intimidation and retaliation.

And where torture is found to have occurred, those responsible must be prosecuted and punished in a timely way, and the victim compensated.

The prohibition of torture has a particular resonance in Cambodia. Many, if not most, Cambodians are linked to someone who suffered torture during the Khmer Rouge period, or have been victims themselves.

Cambodians know only too well the disastrous effects on those tortured, their families and the community.

It is welcome news, then, that Cambodia has made efforts to deal with torture committed in the past and address the risk of torture today.

The trial and sentencing of “Duch” marks the first time a public official has been prosecuted for acts of torture, at least since the Khmer Rouge period. This landmark decision is testament to Cambodia’s commitment to saying “never again” to the coercive use of force to extract information or confessions.

Cambodia is also one of only a handful of Asian states to have ratified the UN Convention Against Torture and its Optional Protocol.

Ratifying the Optional Protocol is particularly significant: governments commit to receive visits from an international sub-committee on the prevention of torture, as well as to establish a national preventive mechanism to monitor all places of detention.

Cambodia welcomed the sub-committee in 2009, providing it with unfettered access to all places of detention, and efforts to establish an independent national preventive mechanism are well under way.

Educating detainees is one way of reducing the risk of torture. Detainees who are aware of their rights are less likely to be ill-treated.

This is why the Ministry of Interior, the Ministry of Justice and the Office of the UN High Commissioner for Human Rights have developed an arrest rights card that spells out, in simple language, the rights of people who have been arrested and taken into police custody.

We hope that this card will be available soon in all Cambodian police stations.

Torture has no place in any society, yet instances of torture continue to occur in all countries, both developed and developing.

Education of officials, lawyers and the public; independent, unannounced monitoring of places of detention; independent, thorough investigations of complaints; prosecution and punishment of torturers: we know these actions reduce the risk of this heinous crime.

The challenge now is to put our conviction into action and to remain vigilant.

James Heenan is the representative of the United Nations Office of the High Commissioner for Human Rights in Cambodia