Garda Commissioner Noel Conroy has appointed a senior officer to re-examine all the investigation files gathered into the 1976 killing of Séamus Ludlow by suspected loyalist paramilitaries with British security forces links.
In a brief statement, An Garda Síochána said the unnamed officer would "reinvestigate where appropriate all avenues of inquiry, with a view to bringing those responsible for this outrageous crime to justice".
The new investigation will require co-operation with the PSNI. The Garda officer concerned will report to Assistant Commissioner, National Support Services, Martin Callinan.
The new investigation was demanded on Wednesday by an Oireachtas inquiry, which had examined an earlier report on the killing from former High Court judge, Mr Justice Henry Barron, and held its own hearings.
In its final report, the Oireachtas Justice, Equality, Defence and Women's Rights sub-committee said the Garda had treated the Ludlow family "in an appalling manner", failing even to notify them of the inquest.
Mr Ludlow was shot three times at close range and dumped in a ditch after he had left a local pub near his Thistle Cross, Dundalk home on May 1st, 1976, though gardaí for a long time believed that he had been killed by the IRA as an informer.
The chief constable of the PSNI, Sir Hugh Orde has already told the Oireachtas committee that there is nothing more that he can do to prosecute the case.
Four men were interviewed in 1998, and two admitted that they were at the scene, but that they had nothing to do with the killing. The Northern Ireland director of public prosecutions believed insufficient evidence existed for a prosecution.
Michael Donegan, one of Mr Ludlow's nephews, said the family did not want a new investigation into the killing because they did not believe that a murder conviction could be secured 30 years on.
However, the family did want a public inquiry to investigate why gardaí did not travel to Northern Ireland to interview suspects in 1979 when they were told about them by the RUC
Furthermore, the RUC should explain why they took 15 months to pass on this information to the Garda, while the British army should be asked to account for its arrest of a family member shortly after the killing, they said.