The families of some of the Omagh victims have said the dismissal by the Special Criminal Court of the case against Colm Murphy was another blow.
The Court today dismissed the case against Mr Murphy, who was charged in connection with the Real IRA bomb in Omagh in 1998.
The blast killed 29 people, including a woman pregnant with twins.
Michael Gallagher, whose son Aiden was killed in the explosion, spoke of his frustration and despair at the outcome.
For the first time in years he said he felt angry. He expressed his frustration at what he felt was the failure of the criminal justice system on both sides of the border.
Mr Murphy had pleaded not guilty to conspiring in Dundalk between 13 and 16 August 1998 with another person to cause an explosion likely to endanger life or cause serious injury to property in the State or elsewhere.
He was jailed for 14 years by the Special Criminal Court in January 2002.
He was the first person to be convicted in the Republic or Northern Ireland in connection with the bombing.
However, in January 2005 the Court of Criminal Appeal overturned the conviction.
This morning, the Special Criminal Court granted an application by Mr Murphy's lawyers for a direction that the prosecution had not established a case.
The court ruled that the fact that notes of the interview conducted with Mr Murphy by Detective Garda Liam Donnelly and Detective Garda John Fahy were falsified combined with the facts that there is no explanation in relation to that falsification, and the fact that this was part of a series of interviews being conducted by three teams of gardaí, taints all the interviews.
It ruled that the accused must be given the benefit of the doubt in this regard.
It ruled all evidence in relation to the interviews was inadmissible and therefore there was no evidence before the court upon which a jury could convict Mr Murphy.
Afterwards, Mr Murphy said he was glad to see it is all over. He also said 'find out who's behind it', when asked for a comment on the fact that no one is now convicted of the Omagh bombing.
Asked if he had any comment on the garda treatment of him, he said 'you heard the court'.
Fine Gael leader Enda Kenny said the outcome was a huge disappointment to the families of the victims of the atrocity who have campaigned so long for justice on behalf of their loved ones.
'The situation now is that nobody stands convicted of the largest single terrorist attack in Northern Ireland,' said Mr Kenny.
'While getting a successful prosecution at this stage will be very difficult, I would urge the security services on both sides of the border to continue to co-operate on this case.
'There are clearly people who have information that can lead to the prosecution of those responsible and I appeal to them to recognise the huge pain that is
The only man to have been charged with their murders, Sean Hoey from south Armagh, was acquitted in Belfast over two years ago.
Michael Gallagher and some of the other relatives later won a civil action in Northern Ireland against four men including Colm Murphy who they claimed were behind the atrocity.
They were awarded damages of £1.6m and that judgement is now subject to appeal.
The PSNI say the book is still open on the bomb investigation.
But 18 months ago the then chief constable said it was highly unlikely there would be a successful criminal prosecution, unless there was a substantial new lead or a new witness stepped forward.