The male in his 50s who was detained at Buncrana Garda Station in relation to the murder of Andrew Allen on February 9 last was yesterday (Saturday) released without charge.
Mr Allen was killed in his home at Links View Park, Buncrana. The father-of-two, originally from the Waterside area of Derry, was the first man to be murdered by the vigilante group, Republican Action Against Drugs.
Gardaí said the man was detained under Section 50 of the Criminal Justice Act 2007.
A file on the matter will be prepared for the Director of Public Prosecutions.