The US Supreme Court will hear Monday a case involving an important medieval art collection that Nazi Germany acquired from Jewish dealers.
The clash centers on gold crosses, jewels and other religious works from the 11th to the 14th centuries that are now on exhibit in a museum in Berlin.
"This case has everything to do with restitution (and) remedying a forced sale, which has major financial implications. But at the heart of it is something that's far more important, which is justice," said Jed Leiber, a musician in California who has sued the German government on behalf of his grandfather.
The latter, Saemy Rosenberg, was an art dealer in Frankfurt in the 1920s.
Shortly before the stock market crash of 1929, Rosenberg and other Jewish colleagues bought the art trove from the duke of Brunswick, a descendant of a European dynasty known as the House of Guelph.
After the market tanked, the dealers managed to sell half of the pieces to American collectors in 1932. The rest they stored in safes in the Netherlands.
In 1935, two years after Hitler came to power, they sold the collection at a low price to Prussia, a centuries-old European state which still existed and was then run by Hermann Goring, who founded the Gestapo.
"It was simply not possible in 1935 for any Jewish business, least of all dealers who are in possession of the German national treasure, to get a fair deal with perhaps the greatest, most notorious art thief of all time," said Leiber.
Germany does not see it this way.
"The Guelph Treasure's sale in 1935 was not a forced sale due to Nazi persecution," said The Prussian Cultural Heritage Foundation, which runs several museums including the one where the disputed collection is held.
Germany bases its argument on the conclusion of a consultative committee that received a restitution request for the trove in 2014.
This committee said that the price paid for the artworks reflected the market at the time and that there was no evidence of pressure from the Nazis for a cut-rate price.
After this opinion was issued, descendants of several Jewish art dealers turned to the US courts to recover the treasure, which they say is worth at least $250 million.
They cite a US law which bars civil suits against a foreign government except when "rights in property taken in violation of international law are in issue."
The case eventually made its way to the US Supreme Court.
The nine judges will examine the case Monday by telephone and issue a ruling by June 2021, which will only address the issue of whether US courts have jurisdiction in this matter.
In a brief filed before the session, the German government said it takes such claims seriously.
"The German government has provided roughly $100 billion (in today's dollars) to compensate Holocaust survivors and other victims of the Nazi era," the brief states.
But it argued that the sale took place between Germans on German soil and that only the German courts can rule in this case.
To decide otherwise, it said, "will have grave foreign policy consequences, inviting a host of lawsuits against foreign sovereigns for their domestic, sovereign acts -- and may prompt other nations to reciprocate, forcing the United States to defend similar actions."
The US government supports Germany in the case.
Lawyers for the plaintiffs counter that "Germany seeks nothing less than sovereign immunity for property taken as part of the Holocaust -- not for this case, but for every case... The Holocaust was not a domestic matter."
"My grandfather was a very proud German citizen," Leiber wrote. "And he was deprived of his citizenship. It was no longer German after Hitler came to power.
"I know there are many legal arguments that will be presented, but just on a human level it doesn't sound like justice. And it sounds like the kind of thing that leads to a denial of Holocaust reality," Leiber said.