MESA, Ariz. (AP) — Nathan Gasch and Martin Hartmann lived next door to each other for four years in a quiet retirement community called Leisure World.

You can tell where Gasch had been six decades earlier by the tattooed number on his arm. Gasch could see where Hartmann had been when he walked into his neighbor’s house and a picture of him wearing a Nazi hat on the wall.

Gasch, a survivor of the Auschwitz concentration camp, saw the picture soon after he first moved in, when Hartmann and his wife invited him to their house in Mesa, east of Phoenix.

“I just walked out of the room,” said Gasch, a soft-spoken 84-year-old with a Polish accent.

But he didn’t notify authorities.

“Maybe I was too childish,” he said in an interview with The Associated Press. “I figured we were living in a community here. I just let it go.”