The men, aged in their 30s, were detained as part of the investigation into the shooting dead of David McCreevey in Tallaght on February 1, 2002.
The men are being held under section 30 of the Offences against the State Act at Tallaght Garda station.
Mr McCreevey was shot dead outside a house belonging to one of his neighbour's at Belgard Heights in Tallaght.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com