CHIANG RAI: Police believe at least two gunmen fired shots in the lethal ambush of a rights activist and leader of the Hmong people and his family in this northernmost province on Tuesday evening. Pol Col Pasawee Chotethianchaiwat, deputy commander of Chiang Rai police, said on Wednesday that investigators at the scene of the attack found spent shells from two kinds of guns, and so believed there were at least two gunmen. Thaweesak Yodmaneebanphot, 54, and his family were on a forested section of the Ban Rom Fa Thong-Ban Pha Tang Road in tambon Por of Wiang Kaen district about 5pm on Tuesday. His wife and young daughter were killed, and Mr Theewesak and his young son wounded. Police found 14 spent 7.62mm shell casings from an AK-47 assault rifle and five spent shotgun cartridges. Investigators said there were many footprints on the road, indicating the gunmen spent time choosing their ambush site beforehand. They had hidden in forest on a hill slope to the left of the vehicle. It appeared the pickup truck had stopped when it was attacked and then reversed for about 15 metres. The gunmen had continued to fire at the truck, bringing it to a halt. Mr Thaweesak's wife Maiyia Wongnapapaisal, 40, and four-year-old daughter died at the scene. He was shot in his right arm and his three-year-old son in his left leg. Police said the family was returning home from their coffee plantation. They were about three kilometres along the road and about five kilometres from their home in Ban Huai Nan, in tambon Por, when they were attacked. Mr Thaweesak is the head of the Hmong Club in Thailand and an important man along that part of the Thai-Lao border. He has actively fought for land rights for people living in forested areas in Thoeng and Wiang Kaen districts.