BERLIN — For three years, Sibylle Ehringhaus, a veteran provenance researcher, worked with the Georg Schäfer Museum in northern Bavaria to examine the ownership history of its 1,000 oil paintings and several thousand drawings, prints and watercolors.

Mr. Schäfer, the industrialist whose collection is displayed there, had bought much of the art in the 1950s in Munich, then a hub for dealers who had had relationships with the Nazis. Among those from whom he purchased works was Adolf Hitler’s personal photographer.

Ms. Ehringhaus’s job was, in part, to determine just how much of the collection had a tainted provenance.

But last year, she said, she began to ask herself why the city of Schweinfurt, which manages the museum, had bothered to hire her.

After she had identified several plundered works, she said, no one seemed to have any plans to return them to the heirs of the original Jewish owners.

Increasingly, she said, she began to feel her work was unwelcome. She was denied access to historical documents vital for her research, she said, and forbidden to contact colleagues at another museum with a research inquiry. So in December she rejected an offer to extend her contract for another year.