Here's an even better documented one (details from Wikipedia):
On 21 September 1943, after being denounced by an acquaintance, Flyweight champ Victor "Young" Perez was arrested in Paris by the Milice Francaise, a French collaborationist paramilitary force of the Vichy Regime. He was detained in the Drancy internment camp before being transported to the German extermination camp of Auschwitz where he was assigned to the Monowitz subcamp to serve as a slave laborer for I.G. Farben at the Buna-Werke.
During his internment, he was forced to participate in boxing matches for the amusement of the German guards and officers. He never lost. By 1945, Perez was one of just 31 survivors of the original 1,000.
To escape from the Russians rapidly advancing on German held territory, the Nazis abandoned Auschwitz in January 1945. On 18 January 1945, Perez became one of the prisoners on the death march from Monowitz in Poland, 37 miles or 62 kilometers Northwest to the Gleiwitz concentration camp near the Czech border. Perez was reported to have been killed three days later on 21 January. According to eye witness testimony he was shot to death by a guard while attempting to distribute bread he had found in Gleiwitz's kitchen to other starving prisoners.
He was inducted into the International Jewish Sports Hall of Fame in 1986. In 2013, his life was made into the French and German-language film
Victor Young Perez. Perez's role was played by the 2000 French Olympic Gold medalist in light-flyweight boxing, Brahim Asloum.
There are only a handful of known Perez autographs out there. This photo has a partial (last name) on the back:
