PARIS (AP) — The Paris prosecutors office on Thursday said that nine people were being detained as part of an investigation into a suspected decade-long, 10 million euro ($11.8 million) ticket fraud scheme at the Louvre, the world’s most visited museum.

The arrests took place on Tuesday as part of a judicial investigation opened after the Louvre filed a complaint in December 2024, the prosecutors’ office said.

The loss for the museum over the past decade is estimated to exceed 10 million euros ($11.8 million), it said.

Those detained include two Louvre employees, several tour guides and one person suspected of being the mastermind, according to the prosecutors’ office.

The museum alerted investigators about the frequent presence of two Chinese tour guides suspected of bringing groups of Chinese tourists into the museum by fraudulently reusing the same tickets multiple times for different visitors. Other guides were later suspected of similar practices.

The prosecutors’ office said surveillance and wiretaps confirmed repeated ticket reuse and an apparent strategy of splitting up tour groups to avoid paying the required “speaking fee” imposed on guides. The investigation also pointed to suspected accomplices within the Louvre, with guides allegedly paying them cash in exchange for avoiding ticket checks, it said.

A formal judicial investigation was opened in June last year on charges including organized fraud, money laundering, corruption, aiding illegal entry in the country as part of an organized group, and the use of forged administrative documents.

Investigators believe the network may have brought in up to 20 tour groups a day over the past decade.

Suspects are believed to have invested some of the money in real estate in France and Dubai. Authorities have seized more than 957,000 euros ($1.13 million) in cash, including 67,000 euros ($79,459) in foreign currency, as well as 486,000 euros ($576,374) from bank accounts.

The prosecutors’ office mentioned a similar ticket fraud is also suspected to have taken place at the Palace of Versailles, without providing further details.

In October, the crown jewels robbery at the Louvre draw worldwide attention to the museum, after a team of four people broke in through a window during visiting hours and fled with an estimated 88 million euros ($104 million) worth of treasures. Authorities have arrested several suspects in that case, but the stolen items remain missing.