The ordnance team found guns and some bullets in the sack, but no explosives.
Officers have also collected other evidence and fingerprints to hunt down the suspect.
Thai Muang Police Station chief Pol Colonel Weerayuth Sitthirattanakun said it is possible that the suspect was afraid of being caught with a cache of weapons and decided to drop them off at the police station.
Police are also wondering if this may have anything to do with the upcoming subdistrict administration elections.