Networks of criminals are trading priceless Middle Eastern antiquities—from entire Roman mosaics to full Pharaonic coffins—on Facebook, and there are no rules to stop them.

The Athar Project, a group of volunteer anthropologists, have released a new report based on their monitoring of 95 Arabic-language Facebook groups where individuals in conflict zones like Syria, Yemen and Libya offer artifacts for sale, including to US buyers. According to their network analysis, one of the most important individuals in the trafficking network is based in Michigan City, Indiana.

The researchers identified several extremist groups, some fighting in Syria and others connected to Al Qaeda or ISIS, that benefitted from these sales. Some managers of the private Facebook groups, for instance, require new members seeking access to pay a tax on the sales generated by their participation. The organizers use the same Arabic term for the tax, khums, that was used by ISIS to profit from antiques trafficking during its brief existence as a state.

“[This] also reveals a more concerning issue: that the institutionalization of antiquities trafficking first established under ISIS was never fully dismantled, it just moved to a new medium,” the report says.

The FBI has warned art dealers that purchasing artifacts plundered by terrorist groups could be illegal. The US government has imposed restrictions on the import of antiquities from Egypt, Libya, Syria and Iraq. The export of such goods is largely illegal in countries across the Middle East. But Facebook has no legal responsibility to prevent these sales as part of the broad immunity technology companies receive for the conduct of third-parties on their platform. The company did not reply to a request for comment about its policies on the trafficking of cultural artifacts by suspected terrorists on its platform.

Participants in the groups also traded knowledge. In one example, members posted Google Earth screenshots of archaeological sites and offered pointers on how best to loot them. Members used Facebook Stories to post images of the antiquities that would be erased in 24 hours, and Facebook’s encrypted chat to communicate. The report says there is reason to believe some of these transactions are conducted on Facebook payments, noting that”admins seeking a khums tax are not going to have the same in-person exchange of goods that the buyer and seller will engage in. Therefore, this payment is likely carried out through a digital transaction.”

All of this activity was monitored and archived by Athar’s ream of researchers. “This is really valuable war crimes evidence that can actually be used in prosecution,” Katie Paul, an anthropologist who is the co-director of the Athar Project, said. “These are links to real people’s profiles.”

In 2015, the International Criminal Court sentenced Ahmad Al-Faqi Al-Mahdi, an alleged member of the Malian Islamist militant group Ansar Al Dine, to nine years in prison for his part in destroying ancient Islamic tombs in Timbuktu. The key evidence in that case, Paul says, was a YouTube video of the destruction, and she hopes the copious evidence she has collected online will help bring justice to others who commit cultural crimes. Facebook, she says, typically deletes these groups when they are identified, instead of preserving the evidence of their activities.

The project’s co-director is the Syrian archaeologist Amr Al-Azm, who has been working to protect his country’s cultural heritage from the conflict that began in 2012. Syria is one of the oldest homes of humanity, with heritage important to Muslim, Christian and Jewish believers as well as vital clues about the history of Roman, Greek and ancient civilizations.

Al-Azm works with a network of people on the ground in Syria to track antiquities theft, and those sources have helped link Facebook postings to real individuals. In several cases, antiquities photographed within Syria or spotted on weapons-trading forums later resurfaced in Facebook’s antiquities trading groups.

More than a third of the posts on these Facebook groups are from users in conflict zones, and 44% were from countries bordering conflict zones, according to Athar’s analysis. The chaos of war prevents domestic governments from enforcing laws against exporting antiquities. Only Egypt has been able to take action on this front, arresting several individuals for selling antiquities on Facebook last year (link in Arabic).

At least one prominent American antiquities dealer was found to be Facebook friends with a Syrian organizer who manages four of these Facebook groups. Paul wouldn’t share the American’s identity but said she reported it to the authorities. It would not be the first time a prominent US collector has been found buying questionable antiquities; The family behind the Hobby Lobby store franchise paid $1.6 million for ancient cuneiform tablets and smuggled them into the US through Israel. They ultimately forfeited the artifacts and paid a $3 million fine.

“High net-worth companies and individuals, if they get caught, they can afford the million dollar fine, and they simply forfeit the assets and continue building their collections elsewhere,” Paul said.

Besides the obvious problems of financing terror groups abroad and the loss of important historical artifacts to researchers, the looting of cultural goods also damages the economic future of these countries. Tourism is a vital part of the Middle East’s economy—before the Egyptian revolution, it accounted for a ludicrous 11% of the country’s GDP. Widespread destruction of famous sites in Syria like the Temples at Palmyra isn’t just a loss to our collective heritage, it will make it that much harder for a future, peaceful Syria to find prosperity again.

Paul began her work on antiquities trafficking doing research on post-revolution Egypt, when activists and archaeologists worked to restore the collection of the Egyptian Museum after it was looted in 2011, sometimes using online tools to ID and track missing objects.

“In doing so, I was searching some of the Arabic key terms for antiquities, and I totally by chance stumbled upon these groups,” Paul said. “Thanks to Facebook’s lovely algorithm, each time I would join one group it would recommend three more.”