The surviving prisoners didn't know what to expect when British troops entered the Nazi concentration camp at Bergen-Belsen in northwest Germany on April 15, 1945.
Nor did the soldiers - until the sight of the naked corpses piled high unfolded before their eyes.
Scenes of the living and the dead in the notorious camp, captured on tape by ordinary soldiers and newsreel cameramen at its liberation, are as relevant now as they were nearly 70 years ago, according to the director of a new documentary.
"The cameramen weren't really there thinking about creating documentary film-making, they were there in a state of trauma and shock just filming what they saw," director Andre Singer told the Thomson Reuters Foundation in an interview.
Sidney Bernstein, a British producer and later founder of Granada Television, was commissioned at the time to assemble the footage into a film that would be a record of the atrocities.
It was to serve both as evidence to show the Germans the extent of the industrialized slaughter, and as timeless testimony to ensure that such crimes against humanity could never be repeated.
More than six million people died during the Holocaust, the genocidal killing of Jews, gypsies and others during the Nazis' rule over Germany and much of Europe.
Ultimately, the footage from Bergen-Belsen was consigned to the archives and the film project was shelved because of changes in the international situation after communist rule was imposed on eastern Europe.
In the documentary Night Will Fall, Singer tells for the first time the history of the planned film using archive footage and eyewitness testimony.
CHRONICLING ATROCITIES
A black and white frame shows human hair carefully sorted in dusted burlap sacks. Piles of spectacles with cracked lenses and mountains of clothes succeed it.
The remaining prisoners at Bergen-Belsen navigate a course between the corpses strewn around the camp, lying in different states of putrefaction.
A typhus epidemic killed nearly 14,000 of the 60,000 prisoners alive when the camp was liberated.
Scenes of battle were filmed from a distance during World War Two, so the close-ups captured by the soldiers at Bergen-Belsen were seen as different, even unique.
Visually explicit images such as those shown in the film become relevant in the broader context of how we document atrocities, Singer said.
Although using atrocity footage in film-making poses a different level of dilemma, it is the only way to have a new public understand what genocide means and why this was the worst genocide in history, he added.
"If you don't (use) atrocity footage it becomes more of an intellectual exercise. You don't shock people enough to take notice," he said.
In April 1994, the world witnessed the death of 800,000 men, women and children in the Rwandan genocide. The United Nations estimated that the three months of genocidal killing was accompanied by the rape of 150,000 to 250,000 women.
"There will always be places and circumstances where mankind will lose any kind of moral compass and will cause more genocide, more trouble, more deaths," Singer said.
"I think the hope is that at least by seeing documentaries like this, by putting them across, every generation will pause before moving onto something else."
Singer also emphasized the need to put atrocity images into context and humanize a story, moving away from "just piles of corpses".
The backbone of Night Will Fall is built on witness testimony that adds depth to the credibility of the archive footage.
"To me by far the most important feature in the film is the characters telling their stories. The documentary should be more than just a history lesson. It should be very much a story about the horror of genocide and mechanisms that we could put in place in the future to stop them," he said.
Night Will Fall opens in cinemas across Britain on Sept. 19.
