Divisional Forest Officer Bidyut Sarkar said post mortem was carried out on the spot and it was found that the elephant, who was keeping unwell for the past few days, had died last night due to ill health.
Its tusks were later cut off by suspected poachers from nearby villages by using crude tools.
Forest department had earlier said that poachers were suspected to have injured the elephant and bludgeoned it before cutting away the tusks.
Sarkar claimed it was the first time that the tusks of a dead elephant were removed in the north Bengal forest.
Conservationists in the area have demanded a CID investigation into the incident while alleging that the pachyderm was killed by poachers.