In 2004, US prosecutors seized a 2500 year of artefact of Iranian origin, believed to have been trafficked.
Since then, due to the US’s deteriorating relations with Iran, the piece has been stored in a warehouse rather than being returned to its rightful owners.
Beyond this point, the case gets somewhat complex & confusing – the end result possibly being that this & other artefacts belonging to Iran may be sold off to provide compensation money for victims of a crime completely unrelated to these artefacts.

From:
New York Times

Antiquities and Politics Intersect in a Lawsuit
By BARRY MEIER
Published: March 29, 2006

INCREASINGLY, the world of antiquities and museums has become a politically charged one, with museums acknowledging that art that was found to be looted must be returned. But when the objects come from a country that is viewed as an enemy rather than an ally, the arena of antiquities takes a different twist. Consider the fate of some artifacts from Iran.

In 2004, federal prosecutors in New York seized a 2,500-year-old silver ceremonial drinking vessel of Iranian origin. Because imports from Iran are severely restricted, a dealer had listed the object on import papers as coming from Syria and sold it to a collector for $950,000.

At the time, authorities heralded the case as part of a broadening crackdown on antiquities trafficking. But these days, they will not discuss the piece’s future or even confirm that it has been stored in a warehouse since its seizure.

It is not clear when, or even if, the ceremonial vessel, which is known as a rhyton, will go back to Iran. But one unrelated development might affect its fate. A group of American citizens, armed with a $300 million court award against the government of Iran, has brought actions against the Oriental Institute of the University of Chicago as well as other museums holding Iranian artifacts. Their goal, unusual as it might sound, is to seize the objects so they can be sold off, thus satisfying at least part of that judgment.

The group of nine Americans received the financial award in 2003 when the Iranian government defaulted on a lawsuit, which was filed in a Chicago federal court, by not defending itself. In that lawsuit, the Americans, who were injured in a 1997 suicide bombing in Jerusalem, charged that Iran had financed its political ally, Hamas, to carry out the blast.

To collect that judgment, however, the plaintiffs have to seize assets belonging to Iran, a task complicated by two factors, a dearth of such assets in this country as well as American legal principles that effectively immunize a foreign government against such seizures.

In this context, the artifacts, which date to the glory days of the Persian Empire, are an inviting target. In the 1930’s, the Oriental Institute, for example, conducted extensive excavations at sites like Persepolis, bringing back thousands of artifacts. Some of those objects were granted to the institute by the Iranian government for its role in the excavation, while others, including a vast library of cuneiform tablets, were lent to the museum for study, with the understanding that they would eventually be returned, said Gil Stein, the institute’s director.

Mr. Stein said it took decades for scholars at the Oriental Institute to decipher the tablets and begin to publish what they had learned about the history of ancient Persia. Finally, in 2003, the institute announced that it had arranged to begin returning some of the artifacts to Iran, information that soon came to the attention of David J. Strachman, a lawyer in Providence, R.I., who represented the plaintiffs in the bombing case.

When Mr. Stein went to work a few days later he got a surprise. “He served us with a summons saying that you need to turn this stuff over in 10 days,” he said.

A legal battle ensued. Both the Oriental Institute and the State Department took the position that the artifacts were part of Iran’s national patrimony and therefore did not fit the definition of a commercial “asset” that could be seized to satisfy a judgment.

Their position, however, suffered a setback in December when an opinion held that only the government of Iran could claim that its assets were immune from seizure, and Iran continues to ignore the legal proceedings. Both the museum and federal officials have asked the judge in the case to set that opinion aside.

Meanwhile, the group of bombing victims has filed claims against a list of institutions with extensive Persian collections, including the Museum of Fine Arts in Boston and Harvard University. Mr. Strachman said he was not interested in fighting a cultural war but simply wanted his clients to get the money that was owed to them.

So far, the only Iranian property his group has seized is a small house in Lubbock, Tex., which the former shah of Iran bought for his son while he was taking flight training in the United States. “If Iran would pay this judgment we would not be here,” Mr. Strachman said.