The carcass of a protected sea turtle was found on Jomtien Beach with at least one indicator it came into contact with humans.
The decomposing reptile had been decapitated and a red string tied around the right front fin.
Authorities suggested fishermen might have towed the meter-long, 60-kilogram turtle to shore Aug. 28, perhaps after it was decapitated by a boat propeller or possibly because they killed it.
The animal had been dead about a week.
Green and Hawksbill turtles, two of four native species of turtles in Thai waters, are both endangered and protected by the Wildlife Preservation and Protection Act of 1992.