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.
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