For the last two centuries, the British Museum in London has claimed ownership of the Elgin Marbles without producing documentation that can establish beyond reasonable doubt that Lord Elgin, a Scottish diplomat, legally acquired the Parthenon sculptures from the Ottoman Empire in the 19th century. Historians have struggled to ascertain the facts in what some consider the world’s most infamous case of cultural theft. Meanwhile, British authorities have consistently denied assertions that the Athenian antiquities could have crossed borders without approval from the Turks, who ruled Greece during the early 19th century.

In a recently completed manuscript entitled Trophies for the Empire, David Rudenstine, a constitutional law professor at the Benjamin N. Cardozo School of Law at Yeshiva University, challenges the British claim to patrimony by arguing against the country’s historical legal defenses. According to Rudenstine, British Parliament committed fraud in 1816 by purposely altering a key document during the translation process, making it appear as though Elgin had received prior authorization from Ottoman officials to remove the Parthenon marbles when he had not.

“From a lawyer’s point of view, this is fraud,” Rudenstine, who was nominated for a Pulitzer Prize for a 1996 history of the Pentagon Papers, told ARTnews. “Parliament has published a report that their translation is a complete and accurate representation of the Italian document, but it’s altered.”

Reached by ARTnews, a spokesperson for the British Museum denied Rudenstine’s claims. “The trustees of the British Museum are entirely satisfied that the Parthenon Sculptures were legally acquired,” the spokesperson said.

After almost 25 years of research, Rudenstine concluded that the basis of the British Museum’s claims to legal ownership of the Elgin Marbles was faulty. And he’s not alone: in recent years, historians revisiting the case have found the United Kingdom’s argument lacking. Scholars of the Ottoman Empire, for example, have said that the language of the Italian document does not match the wording of a typical Turkish contract from that period.

Pressure for repatriation around the world has intensified in recent years as decolonization campaigns have highlighted how European art collections contain objects looted from foreign countries, including Nigeria and Benin. Greece has repeatedly requested the return of the Parthenon sculptures since gaining independence in 1832, and officials in the country stepped up their efforts to bring Greek objects back into the country since the opening of the Acropolis Museum in Athens in 2009. More recently, Brexit has strengthened European support for the Greek cause. Last week, the country inserted a clause into the European Union’s trade negotiations with the United Kingdom that would require the British government to return all its stolen antiquities. (A Greek official reportedly denied that the clause was related to the Elgin Marbles.)

“The more I dug into the issue, the more I began twitching,” Rudenstine said. “The British position just didn’t sound right, and I realized that central to their legal claim was this Italian document.”

Rudenstine has lectured on his findings surrounding the contract over the years, and he wrote a paper on the Elgin Marbles in 2001 that appeared in his school’s law review. Researchers have failed to recover the Turkish version of the document, which is absent from the Ottoman archives, despite the empire’s meticulous record-keeping from that time period. Furthermore, the lawyer’s research showed that Elgin and his agents in Greece didn’t read Italian, which raised the question as to why such a consequential agreement would be written in a language neither party spoke fluently. Rudenstine said he was able to confirm that Elgin’s interpreter was Italian, meaning that that person may have been the intermediary who wrote the document.

Rudenstine also raised the possibility that Parliament may have taken liberties when translating the Italian document. The English version identifies Philip Hunt (an agent for Elgin who worked in Greece) as the marbles’ courier, lists a date for the contract as 1816, and suggests that a Constantinople Ottoman official gave signed approval for the exchange. By contrast, the Italian version includes none of these three items. In place of a name, the latter lists “n.n.”—a Latin abbreviation used to signify an unnamed person, the equivalent of leaving blank space for putting one’s name on a document.

Rudenstine claims that Parliament committed fraud by inserting Hunt’s name into the document, which was later used to legitimize Elgin’s 1816 sale of his marbles to the British Museum at a moment when the public favored returning cultural property to its source nation. One year earlier, Europe had demanded that Napoleon Bonaparte return the national treasures he plundered during his campaign across the continent after the French leader’s Waterloo defeat in 1815.

“By its terms, the Italian document states that the Athens officials should allow Elgin’s agents to measure, draw, and make molds since no harm will come to the famous Greek sculptures,” Rudenstine said. “Thus, it not only fails to give permission to remove the sculptures from the high walls, but states that Elgin’s activities will not harm the sculptures.”

The Italian document is now in the possession of the British Museum, after belonging to the amateur historian William St. Clair for several decades. Rudenstine had a chance to review a photocopy of the contract sent to him by the historian, who is based in the U.K.; since then, the British Museum has not put it on view. (The contract is, however, available to see by appointment, the museum spokesperson said.)

Asked about Rudenstine’s claims, the British Museum spokesperson referred ARTnews to a 2009 paper by Dyfri Williams, an archaeologist who formerly worked at the institution, having been its keeper of Greek and Roman antiquities from 1993 to 2007. In that paper, Williams suggests that Rudenstine is incorrect to suggest that the document was incomplete when Hunt signed it; the “n.n.” area, Williams writes, was typically left blank. In other words, the Italian contract was the “final document,” Williams says, and according to his logic, no fraud would have been committed.

In the paper, Williams concludes that the document, which he calls a royal decree, or firman, is “the official legitimization, after the event, by the responsible authority.”

Rudenstine maintains that British officials acted illegally. “Parliament committed fraud. And when they published the document in English, the government failed to lend clear evidence to support their claim,” he said. “If my argument is true, then the British Museum must return the Elgin Marbles.”