Forest guards heard gun-shots near Borholla camp in the Burapahar range of the park after midnight and on reaching the spot found a dead male rhino with its horns removed.
The forest guards also found empty cartridges of AK-47 and .303 rifles and an axe from the spot.
One person was nabbed from nearby Mazgaon village.
This is the fourth incident of a rhino being killed and its horns removed in the first month of this year in the park, the sources added.