The three pachyderms — one male and two females — were found dead on Wednesday near a village pond outside Kaeng Krachan national park in Prachuap Khiri Khan province.
Police initially thought they had been poisoned by eating pesticide-sprayed crops but they now believe the animals were electrocuted.
Local farmer Sompong Yapakdi, 46, has confessed to putting electrified wire around the village pond to stop the elephants accessing the water.
“He said he used wire to circle the reservoir to prevent the elephants from jumping into the pond,” Major Naruepanat Nujui of Ban Nong Plub police told AFP by telephone.
“He faces charges of killing an endangered or protected animal which carried up to four years jail terms or a 40,000 baht ($1,170) fine,” he added.
Police gave the elephant ages as 10, 5 and 2.
Thailand has roughly 2,500 wild and 4,000 domesticated elephants.
Those in the wild are usually found in national parks but clashes with locals outside those sanctuaries are not uncommon with impoverished farmers keen to protect their crops.
Much of the country is currently experiencing one of the worst droughts in living memory with water for agricultural use restricted.
Last month a domesticated elephant killed a 28-year-old man and injured his colleague as they were eating dinner at a beachside restaurant in the country’s east. – AFP