Descendants of Berlin publisher Rudolf Mosse working with state-funded experts to try to recover thousands of lost pieces

The American heirs of a German-Jewish family have launched an unprecedented partnership with German state institutions to try to recover a vast art collection stolen by the Nazis.

Descendants of the Berlin publisher Rudolf Mosse will work alongside government-funded provenance researchers to seek information from leading art institutions and private collectors about what happened to the thousands of paintings, sculptures, archaeological artefacts, books and other antiquities that were lost.

Mosse, who died in 1920, was a leading figure in Germany’s publishing industry as well as a prominent philanthropist. The Berliner Tageblatt newspaper he founded, as well as a number of other publications, were among the most significant liberal voices against Nazism.

Facebook Twitter Pinterest Rudolf Mosse. Photograph: Alamy Stock Photo

His family were forced to flee Germany and relinquish their property. They travelled via Switzerland to France and later to the US, where they settled in California.

Roger Strauch, Mosse’s step-great-grandson and a member of the Mosse Foundation, said the project was not about retribution towards Germany but about discovering the truth.

“Our first priority is to ensure the remembrance of the Mosse family,” he said. “The second is to make use of the tremendous provenance talent in Germany, who are deeply dedicated to finding the truth about what happened to these works.”

The project, called the Mosse Art Research Initiative (Mari), will pursue the whereabouts of thousands of works now scattered throughout the world. About a thousand works owned by the Mosse family have been identified and listed on the Art Loss register in an attempt to diminish interest from auction houses.

Strauch said major art institutions had signalled their readiness to be involved in the project. He was also hoping to gain the support of the world’s leading auction houses. Strauch insisted they had information about certain works belonging to the Mosse family but were unwilling to cooperate because they had sold confiscated items.

“We’ve been in touch with the major auction houses, and they do know where some of these works are. But they are not going to tell us because they sold them,” Strauch said. “We’re asking them to contact their buyers and let them know that there is a public claim for these works.”

Strauch said the process would be awkward and difficult but was “the important next step in our work”.

So far Mari has used archive information – including a catalogue of Mosse possessions published by Nazi authorities – and the help of private detectives to locate about 36 works.

Facebook Twitter Pinterest Lady with Red Blouse. Photograph: Oskar Reinhart Foundation

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Nine have been restituted – including Susanna, a sculpture by Reinhold Begas, which was found in Berlin’s National Gallery; August Gaul’s Resting Lion from 1903, also found in Berlin; a Roman child’s sarcophagus from the end of the second century AD; and Lady with Red Blouse, a pastel drawing of Mosse’s sister Emilie by Adolph Menzel, found in Winterthur, Switzerland.

Strauch welcomed the German state’s willingness to be involved in what he called “one of the largest restitution projects ever”.

“This is an example of Germany building bridges rather than walls, and I applaud and appreciate their efforts,” he said.

The project comes nearly four years after the reclusive collector Cornelius Gurlitt was found to have kept hidden a huge collection of art for decades. The case led to renewed debate in Germany over how to deal with looted art after it was revealed that Gurlitt inherited much of his collection from his father, an art dealer who traded in works stolen by the Nazis.

Hermann Parzinger, president of the Prussian Cultural Heritage Foundation, one of the main partners in Mari, said: “There was never a question about us being involved in this. It’s also a part of German history that we’re restituting.”

• This article was amended on 8 March 2017. Because of an editing error, an earlier version used the word “ancestors” where “descendants” was meant.