Sotheby’s is suing two Florida consignors and an auction house they own for nearly $7 million after several pieces of furniture and decorative art purported to be by Diego Giacometti allegedly turned out to be fake.

The seven works were sold in separate sales over the course of 2016 and 2017. A handwriting expert determined that the provenance documents the consignors submitted with the lots were forged, according to the lawsuit.

Having canceled the sales and refunded the money to the respective buyers, Sotheby’s now wants the consignors—Frederic Thut, his wife Bettina Von Marnitz Thut, and their business, Fine Art Auctions of Miami (FAAM) —to return their proceeds as well.

The Thuts could not be immediately reached for comment and emails to the Miami auction house did not receive a reply.

As part of a “brazen fraudulent scheme,” according to Sotheby’s, Frederic Thut claimed to have purchased a large trove of works, supposedly by Diego Giacometti, brother of the world-renowned sculptor Alberto Giacometti.

Thut then consigned the works to his own auction houses “with no disclosure concerning his own ownership interest in the works.” The lots were then purchased by Thut’s wife, who soon thereafter consigned them to Sotheby’s at far higher estimates than their sales prices at FAAM, according to the complaint.

Sotheby’s said it discovered the works were counterfeit in 2018 after one of the buyers enlisted an expert, Denis Vincenot, who works closely with the artist’s estate and deemed the purported Giacometti works inauthentic. The auction house claims that Von Marnitz Thut was required to return any proceeds paid to her in connection with the sale once it was canceled.

By its own admission, Sotheby’s initially pushed back on the findings, citing the “strength” of the provenance documents the Thuts had provided. Those included letters from the legendary New York dealer Pierre Matisse and from Serge Matta, brother of Surrealist painter Roberto Matta, as well as a certificate of authenticity by James Lord, author of a book about Alberto Giacometti.

But Sotheby’s employees changed their minds after hiring a handwriting expert. The consultant concluded that the documents purportedly written by Matisse were inconsistent with samples sourced from his archives in the Morgan Library. It was also found that the Matisse, Matta, and Lord documents were all written by the same hand. Finally, the presence of counterfeit protection system coding in the letterhead was introduced to all printers in the 1990s, and therefore could not have appeared in 1982, when the letters were dated.

“Sotheby’s had engaged the handwriting expert to convince Vincenot of the authenticity of defendants’ consignments,” reads the complaint, “only to learn that the documents supposedly proving the provenance were themselves forgeries.”