A man has been arrested in relation to the murder of Stephen Hanaphy in Co Louth in October 2010.
Mr Hanaphy, 20, died after being shot in a row at a house on the Sliabh Breagh estate in Ardee.
The man, who is in his early 20s, was arrested in the Dunleer area at about 7.30am.
He is being detained at Dundalk Garda Station.
During the planned operation, gardaí discovered cannabis plants with an estimated street value of €3,200.
Searches at a second property led to the discovery of illegal cigarettes, with an estimated loss to the State of €200,000.
Illegal alcohol and various distilling equipment were also uncovered.