A 27-year-old suspect was arrested over aiding and abetting the murder of Chief Jailor of the Welikada Prisons Training School, Police said.
The jailor was shot dead in Ambalangoda on August 3.
The police also recovered T56 assault rifle, 63 live ammunition and 15 SIM cards from the suspects' house at Thiranagama in Hikkaduwa.
The Ambalangoda police initially arrested two suspects in possession of 2.8 grams of heroin last Tuesday (13).
They were detained for seven days for further questioning.
It was revealed during the questioning that one of the suspects, identified as Manjula Ranga Kumara, had aided and abetted the shooting at Chief Jailor of the Welikada Prisons Training School Thilina Ruwan Thihara.
The 44-year-old Chief Jailor, who was a resident of Ambalangoda, was killed when he was shot at by unidentified gunmen at Kuleegoda Junction.
Police said the two suspects will be produced in the Balapitiya Magistrate's Court on charges of possessing heroin while the police will also inform the magistrate about Manjula Ranga Kumara over his allege involvement in the shooting.
The Ambalangoda police are investigating.(DSB)