Mrs O'Reilly, a mother of two, died as a result of blows to the head at her home in The Naul last October.
Last year, two men and a woman who were arrested in connection with her death were later released without charge.
Updated: 16:51, Friday, 27 March 2009
A man arrested on Tuesday in connection with the investigation into the murder of Rachel O'Reilly was released without charge from Balbriggan Garda Station in north Dublin last night.
Mrs O'Reilly, a mother of two, died as a result of blows to the head at her home in The Naul last October.
Last year, two men and a woman who were arrested in connection with her death were later released without charge.