The arrest of PNJ Lab's former director in a diamond smuggling investigation has drawn attention to the crucial role certification laboratories play in Vietnam's jewellery market.
Authorities have arrested Dang Ngoc Thao, former director of PNJ Lab, in connection with an alleged cross-border diamond smuggling ring involving more than 28,000 diamonds. PNJ Lab has described the case as "an individual's legal responsibility." The incident has also drawn attention to the role the certification company plays within PNJ's business ecosystem.
From 2024 until the network was uncovered, the smuggling ring successfully carried out 141 shipments, bringing more than 28,000 diamonds into Vietnam. Photo by the People's Public Security Newspaper.
Vietnam's diamond market was shaken after police in Thanh Hoa Province announced they had dismantled a transnational diamond smuggling network and prosecuted 22 suspects.
According to investigators, the group carried out 141 smuggling trips between 2024 and the present, bringing more than 28,000 diamonds from Hong Kong (China) into Vietnam, generating an estimated turnover of VND280 billion (approximately US$10.7 million).
A key figure in the investigation is Dang Ngoc Thao, former Director of PNJ Lab Co., Ltd., a wholly owned subsidiary of Phu Nhuan Jewelry Joint Stock Company (PNJ).
Investigators allege that Thao exploited his expertise in gem certification to facilitate the illegal operation. According to the investigation, he and other suspects purchased smuggled diamonds whose physical characteristics did not match their Gemological Institute of America (GIA) grading reports, allowing them to be acquired at discounted prices.
Authorities allege that the original GIA laser inscription on the diamonds was removed, replaced with new identification numbers under the PNJ Lab system, and accompanied by newly issued certification reports to legitimize the diamonds' origin and increase their commercial value before they were sold.
The investigation remains ongoing. However, the case has intensified public scrutiny of gem certification laboratories, whose assessments play a critical role in determining diamond values and maintaining confidence in the market.
So far, investigators have announced charges against Dang Ngoc Thao in his individual capacity. No information has been released indicating that PNJ or PNJ Lab, as corporate entities, are under criminal investigation in connection with the case.
PNJ Lab, officially known as PNJ Lab Co., Ltd., specializes in the certification of diamonds, gemstones and precious metals. According to PNJ's 2025 consolidated financial statements, the company is a wholly owned subsidiary of PNJ.
As a single-member limited liability company, PNJ Lab does not publish separate financial statements, meaning its revenue and profit figures are not publicly disclosed. Nevertheless, its operating model differs significantly from that of jewellery retailers.
Unlike jewellery businesses that generate revenue primarily through product sales, certification laboratories earn income from service fees. Customers submit diamonds, gemstones or precious metals for examination, after which specialists use dedicated equipment and technical expertise to analyse the items before issuing grading reports or certificates.
In other words, PNJ Lab's core product is not the diamond itself, but the authentication of that diamond.
Its business model relies on certification fees, while its most valuable asset is credibility. A grading certificate only has commercial value when the market believes the issuing laboratory is independent, technically competent and professionally trustworthy.
Certification is particularly important in the diamond industry. Two diamonds may appear nearly identical to the naked eye but differ substantially in value because of variations in colour, clarity, cut, carat weight or evidence of treatment. As a result, grading reports serve as a fundamental basis for pricing, buying, selling and transferring ownership.
According to information previously published by the company, PNJ Lab certifies more than 10,000 items each month, primarily diamonds, including some valued at several million US dollars. This volume suggests that a significant number of transactions in Vietnam's diamond market rely on its certification results.
Beyond generating revenue through certification services, PNJ Lab also supports the broader PNJ business ecosystem. Products accompanied by certificates issued by a laboratory trusted by the market are generally easier to price and trade.
According to company information, PNJ Lab was established in 1998 and has previously stated that it accounts for around 70% of Vietnam's diamond and gemstone certification market. It was also the first gem-testing laboratory in Vietnam to receive ISO/IEC 17025 accreditation for testing and calibration competence.
In early 2016, PNJ invested in additional advanced testing equipment supplied by the Gemological Institute of America (GIA) and De Beers, including DiamondView, DiamondCheck and D-Sure systems, to identify natural diamonds, laboratory-grown diamonds and diamond simulants.
PNJ Lab is also licensed to test the purity of gold jewellery nationwide. Its certification results have previously been used as evidence in disputes concerning gold purity in the domestic market.
Meanwhile, PNJ is Vietnam's largest jewellery retailer. According to its 2025 consolidated financial statements and first-quarter 2026 financial report, the company generated revenue of more than VND35.4 trillion (approximately US$1.35 billion) and net profit of around VND2.83 trillion (approximately US$108 million) in 2025. Total assets stood at nearly VND19.7 trillion (approximately US$752 million) at the end of the first quarter of 2026.
While these figures do not reflect PNJ Lab's standalone financial performance, they illustrate the certification company's importance within the business ecosystem of Vietnam's leading jewellery retailer.
For that reason, the investigation has heightened public attention to the role of gem certification organizations, where the credibility and independence of grading reports are crucial to maintaining confidence in the diamond market.
PNJ shares came under heavy selling pressure during the morning trading session on July 3.
By around 11:04 a.m., PNJ stock had fallen VND4,400, or 6.97%, to its daily floor price of VND58,700 per share. Trading volume exceeded 926,000 shares.
Notably, the stock had no buy orders at the floor price, while sell orders at the limit-down level totaled approximately 11.28 million shares.
Who is the former PNJ Lab director accused in the diamond case?
Former PNJ Lab Director Dang Ngoc Thao. Photo courtesy of PNJ.
Police in Thanh Hoa Province said the former director of PNJ Lab allegedly worked with other suspects to purchase smuggled diamonds whose specifications did not match their GIA grading reports.
On July 2, Thanh Hoa Provincial Police announced they had dismantled a transnational diamond smuggling ring allegedly operated by foreign nationals.
Investigators said the network successfully carried out 141 shipments from 2024 until it was uncovered, smuggling more than 28,000 diamonds from Hong Kong (China) into Vietnam with an estimated turnover of VND280 billion (approximately US$10.7 million).
One of the suspects identified by police is Dang Ngoc Thao (born in 1974), a resident of Binh Thanh Ward, Ho Chi Minh City.
According to investigators, while serving as Director of PNJ Lab, a subsidiary of PNJ, Thao allegedly worked with other members of the network to purchase smuggled diamonds whose characteristics differed from those described in their GIA certificates and were therefore sold at discounted prices.
Investigators allege that, despite leading a well-known gem certification laboratory, Thao used his professional expertise to facilitate the smuggling operation.
Authorities said he allegedly removed the original GIA laser inscriptions from the diamonds, engraved new identification numbers under the PNJ Lab system and issued new grading certificates to legitimize the diamonds' origin and increase their commercial value before they entered the market.
According to investigators, grading certificates play a decisive role in determining the commercial value of diamonds and in building consumer confidence. PNJ Lab operates as an independent certification laboratory and, under applicable regulations, is not permitted to trade directly in the products it certifies.
Police said the alleged conduct not only facilitated diamond smuggling but also seriously affected the reputation of the certification laboratory and undermined confidence in Vietnam's diamond market.
According to information published on the company's website, PNJ Lab evolved from the PNJ Gemological Center, established in 1996 as part of PNJ.
The company provides certification and consulting services for diamonds, gemstones, semi-precious stones, gold, silver, precious metals and non-ferrous metals, and also offers laser inscription services for diamonds. It is equipped with specialized instruments to identify natural diamonds, synthetic diamonds and diamond simulants.
PNJ Lab was the first gemstone testing laboratory in Vietnam to obtain ISO 17025 accreditation. Since February 2015, it has also been licensed by the Directorate for Standards, Metrology and Quality under the Ministry of Science and Technology to certify the purity of gold jewellery nationwide.
On the evening of July 2, the company confirmed it had received information from authorities regarding the investigation involving Dang Ngoc Thao. In its press release, the company referred to him as its former director.
The company stated that the matter concerns "the individual's legal responsibility" and is being handled by competent authorities in accordance with the law.
"PNJ Lab respects the investigation process and will not make any comments beyond the information officially released by the authorities. The company stands ready to fully cooperate upon request," the statement said.
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