Detectives are investigating the find of three firearms and ammunition in the Oldpark Road area of Lisburn on the morning of Wednesday 25 May.
The legally held firearms had been stolen in a house burglary in Newtownards in February 2016.
Just after 9.50am, police received a report that the firearms had been found at the side of the road.
The Oldpark Road was closed between approximately 10.20am and 6pm while ATO attended the discovery.
The firearms and ammunition were later seized by police.
Detective Sergeant James Johnston said: “I would ask anyone who has noticed any suspicious behaviour in the Oldpark Road or Pond Park Road area recently to contact detectives at Lisburn Police Station on the non-emergency number 101.
“Or if someone would prefer to provide information without giving their details, they can contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111.”