The man arrested is being questioned at a Garda Station in the east of the country.
A man in his 40s has been arrested by Gardaí investigating the murder of Kenneth Fetherston.
The 26 year old disappeared in September 2009, and his remains were found in the Dublin Mountains four months later.
Officers from the Serious Crime Review Team and the National Bureau of Criminal Investigation have also searched a house in the midlands.
The man arrested is being questioned at a Garda Station in the east of the country.