Under the radar in Thailand: The foreigner who built an arsenal at home

For two years, Sun Mingchen was a “perfect neighbour”. Living in a 38,000-baht-a-month luxury house at the Maple Housing Estate in Chon Buri’s Bang Lamung district, the 31-year-old Chinese national was known as friendly and polite.

Little did his neighbours know that behind the closed doors of his rented house, Sun was quietly assembling a military-grade arsenal and apparently preparing for something far more sinister.

“He was always friendly and always warmly greeted people,” a resident at the housing estate in Huai Yai sub-district said.

Sun was arrested after his vehicle overturned on the railway bypass road in Bang Lamung on Friday (May 8), prompting a search that uncovered the weapons at his residence. Police are now hunting his possible accomplices.

A trail of deception

Born in Heilongjiang province in northeastern China, Sun entered Thailand in 2020 and almost immediately managed to cheat the residency system. For just 2,000 baht, he was reportedly added to the household list of a hilltribe woman in Chiang Dao who was registering for Thai citizenship.

“I only met him once but agreed to add his name after pressure from an official at the Chiang Dao District Office,” the woman said.

She later removed his name from her documents on the advice of her village head.

Two years later, Sun met and married a Thai woman (identified only as Jantima), using her household registration to secure a pink residency ID card for non-Thai nationals.

The couple split up in August 2025, but Jantima took pity on him.

“I never removed his name from my household book, because I felt sorry for him. I know he has nobody else to look after him here.”

She told police that they spent little time together in her Klong Sam Wa house while married, since Sun preferred to live in Chon Buri. He also travelled extensively, purportedly managing his car-rental businesses in South Korea and Australia, she said.

The suburban arsenal

Police discovered that Sun lived in Pattaya City before moving to the Huai Yai house, where they uncovered the cache of war-grade weapons. The arsenal included two M16 rifles, nearly 5 kilos of C4 explosive, four Russian-made POMZ-2 anti-personnel mines, a Glock 26 pistol and ammunition, 10 M16 magazines, and at least six grenades. It also featured seven detonators, remote controls and fuses for mines, three bulletproof vests, two gas masks, four 20-litre cans of gasoline, and 791 rounds of ammunition.

More alarming still was the discovery of C4 explosives configured for immediate denotation.

Some items were marked with the LOT RTA logo, indicating they were manufactured at a Royal Thai Army ordnance factory.

Shaky plea and shadowy networks

Sun told police that he was a “depressed firearms enthusiast” planning a complex suicide – a claim they quickly rejected.

Evidence recovered from his personal belongings suggests he had high-level security experience. Videos found on his phone show him training at Cambodia’s elite Bodyguard Headquarters, responsible for protecting the country’s top leaders, and using ChatGPT to research sabotage methods and the blast radius of explosives.

Police have arrested a Royal Thai Navy petty officer, a shooting range operator, and three other suspects for allegedly supplying weapons to Sun. Meanwhile, a police-issue Glock pistol found in Sun’s possession was linked to a former Thai cop who is currently serving time in prison for bribery.

National Police Chief Kitrat Phanphet rushed to Chon Buri to personally oversee the case amid concerns over a potential national security risk.

Chance encounter

Sun and his arsenal would have remained a secret were it not for the diligence of a junior policeman who responded to his car accident on a rain-slicked road last Friday. Pol Corporal Nilpat Thongyoi immediately sensed something suspicious in Sun’s demeanor.

“He refused all help and even tried to stop me from calling an ambulance,” the corporal said.

Alerted by this behaviour, Nilpat and his colleagues searched the car and discovered weapons in the boot. “I called for immediate backup,” he said, recounting the moment that triggered the raid on Sun’s fortified home and the secrets it held.

The case has since spiralled into a complex nationwide investigation involving Immigration Police, the Chinese Embassy and foreign security agencies. Sun has so far been charged with illegal possession of firearms, ammunition, explosives and military ordnance, as well as carrying firearms in public without a permit.

By Thai PBS World’s General Desk