In 1962, just four years after Lilly Cassirer received a settlement of $13,000 from the German government for a painting looted by the Nazis, she died.

Cassirer, who was Jewish, fled Germany for England during the Holocaust in 1939, forcibly selling a Camille Pissarro oil painting for $360 in exchange for visas that secured safe passage for her and her family. Cassirer's father-in-law had bought the painting directly from Pissarro's own dealer in Paris, and as Artsy reports, appraisers say that the work, Rue Saint-Honoré, Après-midi, Effet de Pluie — an 1897 impressionist Paris street scene that over time found its way into a Madrid museum — is now worth more than $30 million. Cassirer’s great-grandchildren have now been in a decades-long battle to get it back after a family friend spotted it in Madrid in the 1990s.

On Monday, the U.S. Appeals Court in San Francisco reanimated the family’s 12-year suit against Spain's Thyssen-Bornemisza Museum, reversing a 2015 lower court decision that found the family was no longer the painting’s rightful owner. As the Art Paper explains, the appeals court ruled in part that the legality of the museum’s ownership hinges on whether curators there knew the painting was wrested through a forced sale.

The museum’s lawyer insists to the Associated Press that the museum's patron, Baron Hans-Heinrich Thyssen-Bornemisza, "acquired the painting in good faith in 1976 and the [museum's] foundation, in turn, acquired the painting in good faith in 1993." But Cassirer’s heirs say that the museum's trained experts should have known better in researching the painting's provenance, and a torn label on the back of the painting from the old family gallery in Germany has buoyed their case. “That label on the back means unequivocally that Spain and the museum knew,” David Cassirer, one of the plaintiffs, told the San Diego Tribune.

After leaving Cassirer's hands, the painting made its way through the hands of several U.S. art collectors before a New York gallerist sold it to Thyssen-Bornemisza, a Swiss industrialist and avid art collector. When the baron died, following the negotiations of his Spanish-born fifth wife, Spain purchased his collection for a whopping $338 million and created the Madrid museum that now bears his name. Whether the baron or the museum knew of the illegality of the 1939 transaction remains to be decided, but the plaintiffs say they're confident the court will return the painting to them.

The case was first brought by Lilly Cassirer's grandson and heir, Claude Cassirer, in 2005, and ultimately taken up by his children after his death in 2010. As David Cassirer tells the Associated Press, when they first brought their claim to the Madrid museum, their reaction essentially amounted to "Go ahead, sue us."

“This is a case in which the record is quite clear,” says attorney David Boies to the Daily Report. Boies has been working on the case for the Cassirer family, and sees it as setting a precedent for Nazi-taken art that was sold under duress. “The museum was on notice that the art had been looted.”