Ho Chi Minh City’s bustling jewelry quarter has fallen unusually quiet. Customers aren’t browsing for engagement rings or necklaces anymore. Instead they’re clutching old receipts and certificates, hoping to sell diamonds they no longer trust.

The discovery of what appears to be Vietnam’s biggest-ever diamond-smuggling network has rippled through the industry. Investigators allege more than 30,000 stones worth over 1.5 trillion dong ($57 million) were brought into the country over the past two years, hidden in luggage, shoes and clothing after being sourced in India and routed through Hong Kong.

In gem-certification labs, diamonds were stripped of their original Gemological Institute of America (GIA) laser inscriptions before being re-engraved and issued with reports that overstated their quality, police said, allowing them to be sold at far higher prices. Authorities are still investigating how widely the stones spread through the market, while dozens of jewelry shops have temporarily closed.