Ground-Off Serial Numbers and Fresh Certificates: The Diamond Smuggling Case That Sent Vietnam's Biggest Jeweler to a Five-Year Low

[Ground-Off Serial Numbers and Fresh Certificates: The Diamond Smuggling Case That Sent Vietnam's Biggest Jeweler to a Five-Year Low]

The diamond trade runs on a piece of paper. A graded stone comes with a certificate, and in most cases the certificate number is laser-inscribed on the diamond's girdle. Type that number into a database and you can pull up the stone's carat weight, color, and clarity. The entire market's trust rests on one thing: the stone and the paper matching.

The transnational smuggling case Vietnamese police announced in early July attacked exactly that link. The smuggled diamonds were cheap partly because their actual specifications didn't match the GIA certificates that came with them, which made the papers effectively worthless. Police allege that Đặng Ngọc Thảo, director of the grading company P-Lab, bought up these stones at a discount, ground off the original laser inscriptions, engraved new P-Lab codes in their place, and issued fresh grading certificates. Stone and paper matched again, and smuggled diamonds acquired legal identities. Under Vietnamese regulations, a grading organization is barred from trading the very products it certifies. This was the certifier robbing his own vault.

P-Lab is not some obscure operation. It is a wholly owned grading subsidiary of PNJ (Phú Nhuận Jewelry), Vietnam's largest jeweler. That is what makes the case so damaging for PNJ: the person who went down is the one who issued the certificates.

Thanh Hóa provincial police, working with Ho Chi Minh City police, closed the net in late June, arresting 22 people, and went public in early July. Investigators say the ring had been running since 2024, completing 141 smuggling runs and moving batch after batch of diamonds from Hong Kong into Vietnam.

The ring's division of labor crossed borders. The alleged ringleaders were Indian nationals based in Hong Kong; diamonds were sourced in India, consolidated in Hong Kong, then hidden in carry-on luggage, shoes, and clothing by couriers who flew in without declaring anything to customs. Sales ran through WhatsApp groups where prices came in at roughly one-third below market rates, and deliveries were verified with a code: the serial number on a US dollar bill.

PNJ moved quickly to draw a line: this was one individual's legal liability, not the company's. The two sides describe Thảo's title differently. The police announcement calls him P-Lab's director; PNJ consistently says "former director." Chairwoman Cao Thị Ngọc Dung gave investors three assurances: P-Lab does not trade diamonds, PNJ has no diamond transactions with P-Lab, and none of the smuggled stones entered PNJ's distribution network. The company then set up a special oversight team to watch P-Lab's management.

One governance detail makes the separation less clean. According to Vietnamese media, P-Lab's chairwoman is Thảo's older sister, and she also sits on PNJ's board and its audit committee. She does not appear on either list of defendants police have announced, but a family link running across the parent company, the subsidiary, and the accused is the kind of thing the market cannot stop chewing on.

The day after the news broke, PNJ shares hit the floor limit at the open and stayed locked there for three straight sessions. By July 16 the stock had sunk to its lowest in nearly five years, with roughly a third of the company's market value gone in two weeks. Brokerages have cut earnings forecasts, and some institutional investors have trimmed their positions.

The irony is that PNJ's underlying business has never looked better; profit hit a record high just last year. Analysts estimate diamond-related products account for about a third of its jewelry revenue, and the downgrades reflect not just the case itself but the expectation that consumers will hold off on diamond jewelry. The company wants to buy back shares to steady the price but is blocked for now by regulatory timing rules, so the buying is personal: the CEO and members of the chairwoman's family are purchasing shares in their own names.

The case itself keeps growing. In mid-July, the Ministry of Public Security announced four more indictments: the owners of three well-known Ho Chi Minh City gold and diamond shops, Kim Lý, Ngọc Tâm, and Ngọc Châu Âu, plus a P-Lab appraiser, bringing the total to 31 people charged. Police also revised the ring's estimated haul upward to more than 30,000 diamonds worth over VND 1.5 trillion (about USD 57 million). The most watched defendant is Ngọc Châu Âu's owner Hoàng Thị Thanh Nga, a 2022 beauty pageant runner-up known in the industry as the "crown queen" for her years of sponsoring pageants.

Once the new indictments landed, shutters came down along Ho Chi Minh City's diamond streets: Kim Lý closed for a month citing "renovations," and Ngọc Tâm and Ngọc Châu Âu followed with their own closure notices. The unease actually started in June, when the diamond shop Long Ngọc shut down entirely after customers rushed to sell their stones back and it ran out of cash. Among shops still open, at least one has switched buybacks to IOUs: sell your diamond back, and you wait five to eight months for the money.

The panic on the diamond streets points at something bigger than any one company. Nguyễn Thị Thu Hương, a senior advisor at wealth management consultancy FIDT, put it bluntly to Vietnamese media: these incidents are the surface; underneath is a regulatory vacuum that has existed for years. Vietnam's diamond market still has no unified system for grading, disclosure, or provenance tracking, and the law does not stop a jeweler from setting up its own lab to certify its own goods, so the conflict of interest is built into what the rules allow. She argues the problem is structural: without independent oversight, the same thing can happen at other companies. Her three prescriptions: legally separate sellers from certifiers, build provenance tracking on documentation and electronic records, and write dedicated regulations.

Certificate fraud has surfaced in other markets too. In early 2024, an Italian gemological lab found lab-grown diamonds laser-inscribed with the numbers of genuine GIA certificates. A buyer checking the code online would see the report for a real stone while holding a different one. As industry observers quoted by VnExpress point out, this kind of fraud doesn't break the grading process; it breaks the link between the stone and the report, and no amount of rigor in the process can stop that. For Vietnamese consumers the problem is more immediate: they no longer trust the certificate itself, and that is the hardest thing for this market to repair.

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