The interrogation of Rudolf Höss, Auschwitz’s murderous commandant, had ended for the day at the Palace of Justice in Nuremberg in 1946 when George Sakheim, an interpreter at the Nazi war crimes trials, took some private time to jot down Höss’s most chilling words in a small spiral-bound diary.

“If we do not exterminate the Jewish race completely now, then the Jewish race will annihilate the German people,” Mr. Sakheim wrote in his native German, recording words that Höss said Hitler had spoken about the Nazis’ “final solution.”

More than a half-century later, Mr. Sakheim recalled his encounter with Höss when he was interviewed about his Holocaust experiences by the USC Shoah Foundation.

“I thought he was a monster, I thought he was a degenerate,” he said in 1998. “In my notes, I said he had an anxious look on his face. I was a budding psychologist; he was frightened and knew he wouldn’t make it.”