Hong Kong’s Customs and Excise Department has busted a transnational syndicate that allegedly laundered the equivalent of about U.S.$64 million (500 million in Hong Kong dollars) using lab-grown diamonds falsely identified as naturals, it announced in late December.

The scheme involved companies in both Hong Kong and India that were allegedly exporting low-value synthetic diamonds from Hong Kong to India and falsely declaring them as higher-value natural gems. Proceeds were then sent to the companies’ bank accounts, according to the Indian Express.

Four men—three from India and one from China—were arrested in the mid-December operation, code-named Gem Crusher. They have been released on bail. Further arrests have not ruled out, a statement said.

(Photo courtesy of Hong Kong’s Customs and Excise Department)