A man in his early 50s has been arrested by gardaí investigating the murder of Alan Ryan in September.
He is being detained under the provisions of Section 30 Offences Against the State Act, 1939 at Coolock Garda station.
Ryan, who had served time in prison for firearms offences linked to his membership of the Real IRA, was shot on the afternoon of September 3rd at Grange Lodge Avenue, Clongriffin, north Dublin.
In recent years he had emerged as a key player in the organisation in Dublin, fundraising by extorting publicans and drug gangs.
Gardaí believe one of the Dublin organised crime gangs with whom he had come into conflict was behind his murder.