Elsa Koditschek was living in a prosperous section of Vienna, near the foothills of the Alps, when the Nazis, who had annexed Austria, confiscated her home in 1940. A German officer, a squad leader in the SS, soon moved in.

Mrs. Koditschek, a Jew, was allowed to stay on, in an upstairs apartment, a tenant in her own house for about a year, until a deportation edict arrived ordering her to a bleak, uncertain future in a Polish ghetto. She fled instead, leaving behind her life’s possessions including the only major artwork she had ever purchased, a landscape by Egon Schiele.

For years, she hid in the homes of non-Jewish friends, according to an account she gave in dozens of letters written during and after the war. But she was ultimately desperate enough to seek refuge in the house the Nazis had seized from her, sneaking back in to live there in secrecy and silence with an upstairs tenant.

From there, she spied on the SS officer, Herbert Gerbing, watching through a window as he sat in the garden with his family. Probably unbeknown to her, while she hid upstairs, he was helping with the deportation of Jews across Europe.