In his testimony, Dr. Feinman described growing up in eastern Poland, in what is now the Ukrainian city of Rivne.

The German invasion forced his parents into hiding while the future Dr. Feinman and his brother, who were teenagers, were conscripted into a railroad crew supervised by Ukrainian police auxiliaries working for the Germans.

Once, he picked up a piece of coal that fell off a train. A Ukrainian policeman took him to the train station. Dr. Feinman overheard the Ukrainian calling his German supervisor and asking: “What should I do with him? Should I shoot him?” The Ukrainian was told to give Dr. Feinman 20 lashes with a metal-buckled belt. Fortunately, a group of German mechanics walked in and interrupted the flogging.

In August, 1942, the brothers, who were now 19 and 15, were deported to the Janowska concentration camp in Lvov. “We were stunned.… We knew that it’s going to be something bad,” Dr. Feinman recalled in his video. At the camp, those who couldn’t work anymore were executed in a ravine, the gunshots ringing in the camp nearby. One boy who escaped was recaptured, then flogged and hanged before the entire camp population.

Dr. Feinman’s parents managed to pay off some of the camp’s functionaries to help the brothers run away by getting them transferred to a cleaning squad that worked outside the camp. The family then fled to Zimna Woda, a village near Lvov, hiding for more than a year with seven others inside a farmhouse.

When people came to the house, they would retreat to an underground hideout accessed by a narrow tunnel. A pipe circulated air and the entrance was concealed by manure and rabbit pens. The farmhouse’s caretaker, Julian Ulanowski, was a Polish Christian, a widower with two young children and a Jewish girlfriend who was passing as a gentile.

“Despite his poverty and the constant danger, with police searches of his house and rumours about his children’s caretaker being Jewish, Julian Ulanowski took care of the Jews from the spring of 1943 until their liberation in the second half of July, 1944,” according to Yad Vashem, Israel’s centre on the Holocaust.

The fugitives never went outdoors. They had to worry about disposing of the waste generated by 11 people. They learned to live together, putting up with the snoring and the cramped conditions.

To pass time, Dr. Feinman read German-English textbooks, teaching himself English and then passing his knowledge to the Ulanowski children.

Then, one morning in 1944, they heard a voice above, addressing Mr. Ulanowski in Russian. The Red Army had arrived.

Dr. Feinman said that day felt like being born again, “like a new gift of life.”

He remembered that, one day in Janowska, the camp commandant, Gustav Willhaus, had mocked the prisoners during roll call, saying that they would all die.

But Dr. Feinman survived and, as he concluded in his video, the payback he had on the Nazis was that he went on to have children and enjoy a long, productive life.