A Roman sculpture headed to auction at Christie’s allegedly belonged to dealers of “illicit antiquities.”

The cover lot of Christie’s upcoming antiquities auction in London has come under scrutiny from an archaeologist who claims it once belonged to two dealers known to have traded in stolen artifacts. The auction house maintains that its provenance research is airtight, and plans to proceed with the sale of the 1st-century marble sculpture of the figure of Eros, which is expected to fetch between £500,000 and £800,000 ($641,000–$1 million) at the December 4th auction.

In comments to The Guardian, Christos Tsirogiannis, a professor at the University of Aarhus in Denmark, called on Christie’s to pull the work from its sale, saying:

Here we have the much-advertised due diligence process of Christie’s that has largely failed since it missed the most important part—the connection to [Robin] Symes and [Christo] Michaelides, notorious antiquities dealers connected with numerous cases of illicit antiquities. [. . .] Christie’s should withdraw the piece and contact the authorities [who will] tell them what to do.

In his research, Tsirogiannis said he found four photographs showing that the object belonged to Symes and Michaelides, who had ties to convicted traffickers of stolen antiquities. In 2005, Symes went to prison for flaunting court orders in the sale of an Egyptian statue. Over more than a decade of researching materials related to antiquities trafficking networks, Tsirogiannis has reportedly pinpointed some 1,100 objects of problematic provenance in private collections, auctions, and gallery shows.

In a statement provided to Artsy, a Christie’s spokesperson said:

Following extensive research, we have found no grounds under which title to sell can be questioned. Christie’s would never sell anything having reason to believe has been stolen or inauthentic. We devote considerable time and money to investigating the objects in our care. We consult academic, police, civil, national and international lists of stolen works and when we publish our catalogues we welcome scrutiny to help us ensure our information is correct.