An abandoned pickup truck loaded with 1.4 tonnes of methamphetamine pills found in Wing Chiat district, Chiang Rai, is believed to be linked to the lethal ambush of a Hmong leader and his family in April.

A total of 57 sacks, containing 11,996,000 speed pills and weighing 1,425kg, were found in the back of the Mazda pickup abandoned on the side of the Chiang Rai-Wiang Chai Road, near the Myanmar border, on Monday.

One wheel of the vehicle had fallen off. The driver had fled.

The find was reported to police by local residents, Pol Gen Thanitsak Theerasawat, special adviser to the Royal Thai Police Office, told a media briefing on Tuesday

He said drug smugglers had recently begun using secondary roads in northern areas to avoid police checkpoints on main roads. The pickup may have been heading for Phayao. It was overloaded and this might be why the wheel came off.

The 57 packs of speed pills were all stamped with “Y1" or “999" and believed to belong to a Wa drug trafficking gang, Pol Gen Thanitsak said.  

Pol Lt Gen Poonsap Prasertsak, commander of Provincial Police Region 5, said the smuggled cargo was believed to be linked to another seizure of 9.4 million speed pills in Wiang Kaen district on April 2.

It was also linked to the fatal attack on the chief of the Hmong club in Thailand and his family in Wiang Kaen district on April 24, he said.

Two or more gunmen opened fire on Thaweesak Yodmaneebanphot, 54, the head of Thailand-based Hmong association, and his family in Wiang Kaen district, killing his 40-year-old wife, Maiyia, and their 5-year-old daughter, Thanyaporn.

Mr Thaweesak, also kamnan of tambon Por, sustained a gunshot wound to his right arm while his 3-year-old son, Chaimongkol, was hit in the left leg.

Thaweesak is a local leader who has campaigned for land rights for residents in Thoeng and Wiang Kaen districts and against the illegal drug trade. The Hmong leader had provided information to police about the smuggling of 9 million methamphetamine pills prior to the ambush, Pol Lt Gen Poonsap said.

Maj Gen Supachok Thawatteerachai, deputy commander of 3rd Army Region, said large amounts of illicit drugs had been seized since six drug smugglers were shot dead during a clash with a patrol last December. The ambush of the Hmong leader was linked to recent seizures of methamphetamine, Maj Gen Supachok said.