Josef Lewkowicz, a Holocaust survivor who became a world-acclaimed Nazi hunter, died on Dec. 26. He was 98 years old.

As a teenager, Lewkowicz was sent to the Płaszów camp outside Krakow in Nazi-occupied Poland at the beginning of World War II and the Holocaust. He would ultimately survive six camps in total while in captivity and was the sole survivor of his family.

After the end of the war, Lewkowicz worked with the U.S. military to track down and identify SS leaders who had disappeared.