(CNN)Nina McGehee always knew that her family fled Europe before World War II broke out. But she only recently learned about what they left behind.
McGehee's great-grandfather, Siegfried Laemmle, was a German art and antiquities dealer with a successful business in Munich. He was also Jewish, and like all Jewish art dealers in the Third Reich, he was forced to liquidate his business as part of the "Aryanization" of businesses.
Some Laemmle objects ended up in private collections, others in museums. Most were sold through a Munich auction house under the guise of legitimate sales.
Now, the current head of the auction house is helping return those objects to their rightful owners, including McGehee's family.
A common estimate for the number of works of art looted in the Nazi era is 600,000 with at least 100,000 still missing.
Often, in the process of restitution, the burden is on families to prove an object was sold because of Nazi persecution. That's starting to change as countries and institutions strengthen their commitments to researching the provenance of objects in their possession and making that information publicly available.
A central database contains an estimated 25,000 missing, looted or identified objects -- paintings, drawings, antiquities -- from more than 15 countries.
But Neumeister Auctions in Munich appears to be one of few private art dealers in the world taking the work upon themselves.
"I'm not responsible for what happened in National Socialism (Nazism), but I'm responsible for what I'm doing now -- or especially what I'm not doing," said managing director Katrin Stoll, who took over the business in 2008.
"As a German business, we have a social responsibility to do this."
Stoll and McGehee shared their story this week at the University of Denver's Center for Art Collection Ethics, where McGehee recently audited a class on provenance research. Toward the end of the semester, McGehee revealed to the professor her connection to the subject.
"It's a wonderful success story that shows the benefits of the kind of research that we're trying to promote," said associate professor Elizabeth Campbell.