A 39-year-old suspect had been arrested by the officers of the Mahabage Police in Ragama with a firearm and ammunition during a raid.
Police said intitially the suspect was found in possession of 1 gram and 800 milligrams of heroin.
Subsequent questioning revealed more alarming discoveries, including a T 56 firearm, 125 live ammunitions, four bullets and 18 9mm live ammunitions.
The suspect, a resident of Peralanda, Ragama, remains in police custody while Police probe the matter further.
