In the years following World War II, Reinhold Hanning had enjoyed a relatively normal life in Germany. He looked on as many of his superiors during wartime, including high-ranking Nazi Party officials stationed at Auschwitz, were convicted in the Nuremberg trials from 1945 to 1949 for their crimes against humanity. But Hanning, a former SS guard, was not considered a high-profile war criminal, so he was never indicted.

That is, until three years ago. In accordance with Germany’s lifted statute of limitations for the prosecution of war criminals, Hanning, who was then 94 years old, found himself face-to-face with justice in June of 2016 when he was charged with 170,000 counts of murder—approximately the number of people who died during his tenure as a sergeant at the death camp.

But proving Hanning was an accomplice to murders that occurred 70 years ago—in a crime scene that has since been destroyed, along with almost all pertinent records—was a tall order. Contributing to the morass was Hanning’s claim that he never personally witnessed victims being gassed to death. Prosecutors needed evidence to link Hanning to the charges in his indictment: monitoring ­arriving prisoners as they were sorted into groups headed directly into labor or the gas chambers, a process that came to be known as “selection.” Essentially, the court needed to travel back in time and see what Hanning saw, from the perpetrator’s vantage point.

That’s how virtual reality wound up in the courtroom, for the first time, in what might be the last World War II Nazi trial. David Freid’s short documentary Nazi VR details how a team of German forensic VR engineers recreated a 3-D model of Auschwitz-Birkenau through millions of laser scans, historical blueprints of the site, aerial photographs, and witness testimonies. Wearing the VR goggles, investigators and judges can climb the watchtowers and observe how prisoners would have been moved around the 15-mile camp, where more than 1.1 million people were murdered during the war.

“Virtual reality is a great tool to objectively establish what was visible to the defendant,” says David Scheffer, who served as the U.S.’s war-crimes ambassador from 1997 to 2001, in the film. “So, as Mr. Hanning claimed, ‘I was in such a position that I could not have seen what was occurring elsewhere in the camp,’ the VR will contradict that claim.”

As Freid’s documentary reveals, the reconstructed model indeed refuted Hanning’s claims. In the court decision, the judge explicitly referenced the VR experience as having aided his ability to establish accountability.

“Technology reveals the memory of what occurred 70 years ago,” says Scheffer. “Hanning represented the common man in the killing machine. Only a very small fraction of those individuals have ever faced justice.”

Freid told me that while making the film, he was moved by the experience of entering the digital camp. “I was also taken by the lengths at which Germany tries to remember its past, and to make sure young people learn from it. I think we need to do a better job of that here [in the U.S.]”