An Oireachtas sub-committee will begin a public inquiry in January into the 1976 murder of Co Louth man Seamus Ludlow.
The RUC told the Garda in 1979 that it believed four named loyalists were involved in his killing, but this information was not pursued by the Garda at the time.
A report by Mr Justice Henry Barron released last night sharply criticised the Garda investigation into Mr Ludlow's death.
No one has ever been charged with the murder of Mr Ludlow (47) who lived at Thistle Cross near Dundalk. He was shot dead early on May 2nd, 1976, as he went home from a night out. He had no connections with any subversive organisation, according to the Barron report.
TDs involved in next year's sub-committee investigation warned last night that senior Garda officers of that time and today would face "very tough questions".
Garda Commissioner Noel Conroy last night accepted that there "were issues" in the original investigation. "In recent years, An Garda Síochána has taken whatever actions were available to right the situation and in this regard co-operated fully with the Barron and other inquiries and will continue to do so," he said.
The RUC told the Garda in 1979 that it believed that Paul Hosking, William Long, Seamus Carroll, and a then UDR corporal, James Reid Fitzsimmons, were involved in the murder. However, they were never questioned in Northern Ireland by the Garda. The Barron inquiry concluded that senior Garda officers feared they would have to allow the RUC the right to interview suspects in the Republic in return.
Mr Justice Barron said it was "most probable" that then deputy Garda commissioner Laurence Wren made the decision not to pursue the RUC's information. This has provoked a furious response from Mr Wren, who has threatened "corrective action to clear my name". Mr Wren, who retired in 1987, said: "I have no intention of accepting the conclusions reached by the inquiry in reference to my supposed activities."
The Barron inquiry carries full Dáil privilege because it was published last night by the Oireachtas Committee on Justice, Equality, Defence and Women's Rights, chaired by Fianna Fáil TD Seán Ardagh.
A sub-committee will now hold public hearings into the report, interviewing as many key witnesses as possible - as it did following Mr Justice Barron's report into the Dublin-Monaghan bombings. It will not be able to compel witnesses to attend.
The 100-page report, which found that some Garda files had gone missing while other information was never stored at all, was sent 14 months ago by the judge to the Department of Justice. However, it was not released until yesterday, the Minister for Justice earlier told the Dáil, because of the decision to name the four suspected killers.
