BERLIN (AP) — Several German cultural institutions and the American heirs of a German-Jewish family have embarked on a joint effort to restitute a vast art collection stolen by the Nazis.

The representative of the heirs, Roger Strauch, told reporters in Berlin on Tuesday that the project to identify and locate the more than 1,000 pieces of stolen art once belonging to the famous Berlin newspaper publisher and art magnate Rudolf Mosse is unique because all sides have agreed to cooperate.

The project is called the Mosse Art Research Initiative.

In many other restitution cases, the family heirs' demands for the return of the art lead to conflicts with the current owners — usually museums or private collectors — who don't see strong enough proof to hand over the disputed pieces.