The High Court this morning upheld a challenge by 36 gardaí to the Oireachtas sub-committee into the shooting dead of Mr John Carthy in Abbeylara, Co Longford, last year.
The judgment said the conduct of a public inquiry held by members of the Oireachtas under the aegis of the Houses of the Oireachtas "liable to result in findings of facts or expressions of opinion adverse to the good name, reputation and or livelihood of persons not members of such Houses" is outside the authority of such Houses.
The ruling was delivered by a three-judge divisional court led by President of the High Court Mr Justice Morris.
The gardaí had disputed almost all aspects of the work of the sub-committee, including its powers to compel the attendance of witnesses and to direct the production of documents.
The gardaí claimed the sub-committee has embarked on a wide-ranging inquiry into the shooting itself rather than adhering to an examination of the commissioner's report into the shooting.
Mr Carthy was shot four times by members of the Emergency Response Unit after a 25-hour siege at his home on April 20th, 2000.
The challenge opened on July 17th for nine days. It then resumed after the court vacation on October 2nd and concluded on October 15th.
Mr John Rogers SC, for the gardaí, had told the court the sub-committee had sought to inquire into whether the last shot fired at Mr Carthy - understood to be the fatal shot - should have been fired at all.
Lawyers for the State have responded the Oireachtas has power to establish inquiries into matters of major public importance and the courts should be slow to trespass on such power.