The first inkling of trouble came when a customs agent arrived at the door of the San Diego Museum of Art in 2004.
The agent carried a subpoena and, to the museum's chagrin, news that one of its 18th-century paintings was stolen property.
The painting ultimately returned home to Mexico in 2006, five years after its purchase from an art dealer, and the museum strengthened its policies regarding the acquisition of art. "We're no longer going to take things that people say for granted whether they sell or donate an object," says museum director Derrick Cartwright. "What's really at stake is the public trust."
But as American museums deal with the fallout from more scandals over stolen and looted art, it's not clear if others are as willing to drastically shake up how they do things.
"Clearly we are not really policing ourselves, otherwise we would never be in this position today," says Marie Malaro, a former attorney for the Smithsonian Institution in Washington, D.C. "Our large museums should know better."
A number of museums have recently faced questions about stolen works:
* In widely publicized raids this year, federal agents confiscated Asian artifacts from four museums in California, alleging the works were stolen.
* Last summer, the Getty Museum in Los Angeles agreed to return 40 allegedly stolen works of art to Italy; a former Getty curator continues to face charges in Italy of trafficking in stolen art.
* In January, New York's Metropolitan Museum of Art returned to Italy a stunning ancient Greek bowl known as the Euphronios krater. Italy alleges that it was looted almost 40 years ago.
The scandals "are a shame," says Ms. Malaro, professor emerita from George Washington University. "[They] blacken everyone's reputation."
Meanwhile, Greece is stepping up its efforts to push the British Museum to return the famed Elgin Marbles, which once decorated the Parthenon. And the issue of artwork that was possibly stolen during the Nazi era still plagues museums across the world.
Many cases revolve around the provenance of antiquities - their history from the moment they were dug out of the ground.
In many cases, it's impossible to find a pristine record of where they've been, says Patty Gerstenblith, who specializes in antiquities law at DePaul University in Chicago. Looters can easily dig up antiquities and claim that they were allowed to leave their home country in Europe or Asia.
Ms. Gerstenblith says some museums do check ownership records to make sure the items were out of their home countries for a long period of time. That fact lessens the possibility that they were recently stolen.
According to her, many museums abide by guidelines set by an international convention and don't buy antiquities without proof of ownership going back to at least 1970. But some curators, she says, won't bat an eye at artifacts that could have come out of the ground within the past decade.
"Museums have not been sufficiently distancing themselves from contemporary looting," she says. "Some of the major museums have been willing to buy things without a real paper trail."
In San Diego, the Mingei International Museum - one of four California museums raided in January - is waiting for the resolution of a case alleging that it accepted smuggled artifacts from Thailand's ancient Ban Chiang period. …