On a cold, gray morning in February, Irene Weiss was waiting patiently in the courtroom in Detmold, a small city in northern Germany. She had come a long way from her home in Virginia to testify in the trial of Reinhold Hanning, a former Nazi SS guard. The trial was off to a late start because Hanning, 94, was waiting for a wheelchair to take him into court. Because of Hanning’s health and age, the trial was restricted to only two hours of court time, two days per week. Every delay meant the 85-year-old Weiss might have to stay in Germany longer than she had planned. And she had already been waiting for this moment a very long time.

Finally, Hanning was wheeled through the entrance in a jacket, glasses and a canary yellow sweater, his chin pressed down into his chest to avoid looking into the cameras wielded by dozens of journalists in the courtroom. It was difficult to imagine that the frail old man had once been a young guard at Auschwitz. Hanning had been charged with being an accessory to murder in the deaths of 170,000 people killed at the death camp while he served there from January 1943 to June 1944. Weiss, who was a 13-year-old Jewish prisoner at Auschwitz during that period, and whose family was killed at the camp, was one of several witnesses testifying in the case brought by a city prosecutor in northern Germany.

Weiss doesn’t remember Hanning personally. None of the camp survivors who have testified at the trial do. But to the court at Detmold, that didn’t matter. They were there to paint a picture of what it was like in Auschwitz, and what role Hanning would have played as one of the thousands of SS personnel who served there. Thanks to a new legal strategy meant to hold even low-ranking ex-Nazis broadly responsible for the Holocaust, it’s become easier to prosecute cases against aging ­defendants—even without evidence of what specific acts individuals like Hanning may have committed more than 70 years ago.