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,” 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, 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.”

Höss, who confessed that more than two million Jews had been gassed at Auschwitz from 1941 to 1943, was a defence witness for senior Nazi officials at the trials. He was later tried in Poland and hanged at Auschwitz.

Sakheim, who died on December 5 at 96, was one of the last surviving interpreters — there were about 30 — at the International Military Tribunal, as the trials were officially known, and an eyewitness to its landmark legal proceedings. Only one Nuremberg prosecutor, Benjamin Ferencz, is still alive.

Sakheim’s death, at a hospital in Lansdale, Pennsylvania, near his home in Gwynedd, was confirmed by his son, David, who said the cause was pneumonia and a heart infection.

In the interrogations of Nazis like Höss and Hermann Göring, Hitler’s deputy, Sakheim played a part in confronting them with incriminating evidence, “often in the form of captured wartime documents that they themselves had signed”, he wrote in The Jerusalem Post in 2015.

During his time in Nuremberg, Sakheim translated German documents into English; interpreted the interrogations of Höss and other Nazi leaders; and provided simultaneous translation of testimony during the trials in Courtroom 600.

At one point during his trial, Höss complained that Sakheim had not correctly interpreted his words and asked that he be replaced.

“My dad said he was mortified to be corrected like that,” David Sakheim said over phone. “But most of the time there were no such corrections, and he was very proud of the fact that he had been able to master that art.”

Recalling one of the interrogations of Göring in the USC Shoah interview, Sakheim described him as “a very large, intimidating man, with big jowls, who looked like he had lost weight”, adding, “He wasn’t getting the gourmet food in prison that he was used to.”

In that particular interrogation, Göring was asked not about the systemic murder of Jews but about military matters, in particular Germany’s aerial attacks against England.

“Göring sought to portray himself as someone who had tried to persuade Hitler against various excesses, such as the firebombing of London,” Sakheim wrote in The Jerusalem Post. Göring, he recalled, had said: “I told him time and time against that we must destroy the English war industry instead of wasting our bombs dropping them on that stupid London.”

Ruben Gabriel Sakheim was born on June 12, 1923, in Hamburg, Germany, to Arthur and Anuta (Plotkin) Sakheim. His father was a playwright and the artistic director of the city’s Thalia Theatre. His mother was a bank clerk.

After his father’s death in 1931, Ruben and his mother moved to Berlin, where she worked as a book editor. But two years later, after Hitler became Chancellor, they left for Palestine and settled in the Tel Aviv area.

His mother bought a car and became a taxi driver and a tour guide, placing Ruben in foster care with two different families over two years. By 1936, she had started making plans to send Ruben to live in Manhattan with his aunt, a doctor. He arrived in 1938; within a year, his mother died of ovarian cancer.

“One day, one of my letters to her was returned, stamped ‘Deceased,’” he said in the Shoah interview. “The next day I got a telegram from my mother’s girlfriend, who said that she couldn’t go on and took an overdose of sleeping pills.”

He was a teenager when he moved to New York, where he changed his first name to George (after George Washington) and replaced his middle name with his father’s given name.

After graduating from high school, he supported himself as an elevator operator and a counterman at the Nedick’s hot-dog stand in Penn Station while attending Columbia University. But his pursuit of a degree in psychology was interrupted when the army drafted him in 1943.

Because he spoke German, he was sent to Camp Ritchie in Maryland, where he went through a training programme in interrogating prisoners of war, reading maps and analysing aerial photographs.

He fought in Normandy, landing about a week after D-Day. As his unit moved east toward the Netherlands he began to translate interrogations of German prisoners — initially to find out where the Nazis were producing V-1 missiles and V-2 rockets, but also to learn the locations of minefields, enemy artillery and tanks.

In early April 1945, as part of the 104th Infantry Division, Sakheim was among the soldiers who liberated the Dora-Mittelbau concentration camp in Nordhausen, Germany. The streets and crematories of the death camp were filled with corpses.

“Walking around the camp, this could have been me if my mother hadn’t decided to move us out of Berlin in the spring of ’33,” he told Jewish Exponent, a weekly newspaper, in 2015.

Sakheim continued to help with the interrogation of German prisoners in internment camps after the war in Europe ended. But he delayed his return to the US when he learned that the coming war crimes trials needed bilingual interpreters.

After flying to Nuremberg, Sakheim, then only 22, moved into the Grand Hotel, which had been partly destroyed in bombing during the war.

After seven months in Nuremberg, he resumed his education. He earned bachelor’s and master’s degrees in psychology at Columbia and a PhD in clinical psychology from Florida State University.

He then began a long career in psychology, holding positions at hospitals, schools and other facilities in Maine, Massachusetts and New York. He specialised in helping teenagers, especially in reducing their risk of suicide.

As the chief psychologist at the Cottage School in Pleasantville, New York, in the 1970s and ’80s, he tried to develop a profile for child arsonists. He also wrote Firesetting Children: Risk Assessment and Treatment (1994), with Elizabeth Osborn.

In addition to his son, he is survived by his wife, Ilse (Oschinksy) Sakheim; his daughter, Ruth Sakheim-Kitchell; and five grandchildren.

Long after the Nuremberg trials, Sakheim wrote that the contents of his diary remained haunting reminders of what he heard from Nazi war criminals face to face, more so than the official transcripts of their testimony.

“Despite the fact that I now have more than 50 years’ post-Nuremberg experience as a clinical psychologist behind me,” he wrote in The Jerusalem Post, “I continue to wrestle with what the perpetrators did, what they said to us under questioning, and how they said it.”