Mount. NABI(マウント・ナビ)

In October 2013, several video cameras and 8 bodies of men and women were found in the mountain known as "Mount. Nabi" located in the Chubu region of Japan. Many of the investigators fainted at the scene as the bodies were gruesomely decapitated by the wild animals. A police investigation was carried but the killer was never found till this day. What happened in the depth of a mountain?