The following is an excerpt from remarks delivered by Kenneth Roth, Executive Director of Human Rights Watch, during the 2017 Nuremberg International Human Rights Award.

We have gathered here today in recognition that there was another, hidden element of President Bashar al Assad government’s atrocities that was in place even before the conflict began. Beyond bombing and besieging people, the government also detained, tortured and executed them. Other detainees died from starvation and rampant disease. Those atrocities took place behind prison gates, often in detention facilities run by the notorious security agencies, the mukhabarat.

Human Rights Watch, my organization, has documented 27 separate detention facilities run by the mukhabarat. These are located around the country, but many are in Damascus, the capital. Thousands upon thousands of people have disappeared into the hellish existence of these detention centers. Some have been released to tell of the horrors inside, but the Assad government tried to cover up as much as it could, so the scale of these atrocities remained for a long time largely unknown.

One irony of the Syrian war is that while the Assad government flouts the most basic rules of international humanitarian law, it never openly admits doing so. It denies that it barrel bombs or gasses civilians. It pretends that it lets necessities reach people in besieged areas. And it bars independent access to the worst of its detention facilities where the bulk of the torture and execution takes place.

It is in that context of denial that the Caesar photos are so important. No one seeing the photographs of more than 6,000 brutalized corpses can deny that something utterly inhumane has been taking place inside that closed prison system. Survivors can describe that hell on earth, but the photographs speak with an unimpeachable directness that compels us to understand the utter cruelty of the Syrian detention system.

The photographs were mostly taken on the grounds of two military hospitals in Damascus. There were so many bodies that the morgue overflowed, so many of the photographs were taken in a hospital garage.

It took an act of immense courage for the photographer – the man known by the pseudonym Caesar, an official forensic photographer for the Military Police – to sneak these photographs out of the country. As a daily witness to these atrocities, he knew all too well how quickly he would join the corpses he photographed should anyone ever catch wind of his plans. His photographs leave no doubt about the magnitude of Assad’s crimes.

And these photographs represent the dead from just some of Assad’s detention victims. Others were killed beyond the roughly two years represented in the photographs, or were sent to hospitals other than the two where Caesar took his photos. Syrian activists have documented well over 100,000 detainees since the March 2011 peaceful uprising that sparked today’s repression and war.

Still, in its inimitable fashion, the Assad government denied that the photos showed what they showed. Maybe these were random battlefield deaths. Maybe they were a macabre collection. Maybe they were someone else’s torture and execution victims.

Because of the importance of shutting off such potential cover stories, Human Rights Watch undertook an investigation to try to understand who the people were in the photographs and under what circumstances they died. We interviewed 37 former detainees who saw people die, as well as four defectors who worked in Syrian government detention centers or the military hospitals where most of the photographs were taken. We also used satellite imagery and geolocation techniques to confirm where the photographs had been taken. Finally, we tracked down 27 families of the victims who were able to identify their loved ones in the photographs and describe how they had last been seen being arrested or led into detention. All of this evidence provided important corroboration for the account that Caesar provided for his photographs.

Notably, all of the 27 families we interviewed said they had spent months or years searching for news of their loved ones, in many cases paying huge sums to contacts and middlemen employed in various government or security agencies. Only two eventually received death certificates which said the deceased had died of heart or respiratory failure – a typical excuse, according to Caesar. None received the bodies of their relatives for burial. That was an added cruelty of the Assad prison system.

All evidence by its nature is backward-looking, but the Caesar photos compel us to act in the future. First, and most important, they highlight the importance of opening Assad’s prisons and releasing his prisoners, since we must assume that these prisons continue to produce more corpses that Caesar’s replacement may now be photographing. Sadly, Assad’s prisoners have received relatively little global attention. The “de-escalation zones” now being negotiated are reducing the killing in at least some parts of Syria. The besieged areas have many humanitarian agencies trying to overcome the obstacles erected by the Syrian government and other armed groups.

But who is looking out for the prisoners? Their fate seems to be little more than a footnote as negotiators convene in Astana or Geneva. We should be shining the Caesar photos on the White House and the Kremlin, on U.N. headquarters in New York and the Palais des Nations, until the fate of today’s prisoners moves to the center of international concern. Today’s ceremony helps in that spotlighting process.

The Caesar photos also compel us to think of justice. That is why Caesar was such an appropriate recipient of a human rights award from this city, Nuremburg, which has become a global symbol of justice for the worst human rights crimes. The sheer magnitude of the horrors photographed by Caesar serve as a declaration that war crimes – indeed, crimes against humanity – have been committed, and that justice must be done.

We don’t yet know exactly what mechanism will be in place to secure that justice. Because Russia has blocked U.N. Security Council efforts to give the International Criminal Court in The Hague a mandate on Syria, the U.N. General Assembly, where there is no veto, did something unprecedented last December. It voted overwhelmingly – by a vote of 105 to 15 – to circumvent the Russian veto and establish an investigative body, the so-called IIIM, to gather evidence for ultimate prosecution. The Caesar photos will likely be a central part of that dossier.

I met last week in New York with Catherine Marchi-Uhel, the French prosecutor who is heading the IIIM. I have preparation confidence in her dedication and ability, but strong political and financial support to the IIIM will be essential for it to succeed.

Some national prosecutions of lower-level offenders have already taken place in several countries including Germany and Sweden under the concept of universal jurisdiction. Theoretically, a future Syrian government might still consent to the jurisdiction of the International Criminal Court, or Russia might refrain from using its veto. One possible route to justice at the highest official levels could again run through the U.N. General Assembly, with it taking the novel step of launching a tribunal for Syria, much as it already established a team of investigators.

Whatever the mechanism, the Caesar photos will help to ensure that senior figures of the Assad government and others in the chain of command are prosecuted not only for bombing, gassing and besieging civilians, but also for the horrors they visited on those held in detention. We all owe Caesar our deepest respect and admiration for his courageous delivery of this evidence to the outside world. The duty now lies with all of us to see that the crimes he documented are promptly brought to an end, and that the people who ordered them are finally brought to justice.

The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Syria Deeply.