Poachers killed the elephant and sawed off its trunk, they said.
The member of Daying Ering Wildlife Foundation Eco-Development Society (DEWFEDS) saw the carcass and informed the Pasighat divisional forest officer (DFO) Tabang Jamoh about the death of the elephant in the area.
Forest officials found the carcass with bullet hole on the forehead, sources said.
The elephant with approximate age of 35 years was killed nearly a week ago, sources said, adding that an FIR has been lodged at Mebo police outpost.