JERUSALEM – Zvi Shefel recalled the day the German army arrived at his Polish town of Slonim in the summer of 1942. The soldiers immediately began mass exterminations and eventually killed more than 25,000 Jews, including his mother, father and sister.

There is nothing in that town that Shefel, 86, can find about his family, he said while attending the Yad Vashem Holocaust memorial Thursday for the "Day of Remembrance" commemoration of the 6 million Jews killed in the Nazi genocide of World War II.

"I've visited all the archives in Belarus to find the names of people, but they weren't there because the archives of Slonim were burned by the Germans when they retreated — but we have to keep the memory of what happened in order to never forget," he said....