Check the tattoo number, all “inmates” of the death camps were tattooed. I had an experience one day when a former survivor showed me his tattoo, a number on his arm. it was very humbling.
Don't rely on that. I had a supervisor back in the day that had a number on his forearm. It was in the right place. He was old enough to have been in the camps if he was a child at the time.
I always figured he was a camp survivor. One day the curiosity got the better of me and I commented on the unusual tattoo. He told me he got it in the Navy when he was on shore leave in San Diego. Him and his buddies were drunk and wanted to get tattooed. He couldn't figure out what he wanted so he opted for his SSN. He never thought about what it would look like.