The body of watcher Kannan was found floating in a well in Mavanalla village in Mudumalai Tiger Reserve, 30 km from here, this morning by the locals.
Quoting preliminary investigations, police said Kannan was allegedly beaten to death by some persons who later dumped his body in the well.
Kannan had prevented some persons from taking the male elephant named Rivaldo, a pet among the villagers, as they used to feed it after part of its trunk was cut off by poachers some time ago.
Some people tried to take the pachyderm to a tourist spot, last evening when Kannan prevented them, following this they allegedly attacked him fatally, police said.
A local tribal, who along with friends used to take tourists to the resort, had been taken into custody for suspected role in the murder and was being interrogated, police added.