The Court of Criminal Appeal has overturned the conviction and life sentence imposed on Paul Ward for the murder of the journalist Veronica Guerin.
Ward remains in jail on foot of a 12- year sentence for his part in the 1997 Mountjoy prison riots.
The three-judge court yesterday found the State's evidence showed Ward did not participate in the planning of "this atrocious crime", and there was no evidence to support the non-jury Special Criminal Court's finding that he had.
Nor was there evidence to support its finding that Ward's role was to dispose of the gun and motorcycle used.
Testimony from a State-protected witness, Charles Bowden, did not support the Special Criminal Court's findings, the court ruled.
In finding Ward's role was to dispose of the gun and motorbike, the Special Criminal Court appeared to have been misled by confusing evidence and voluminous documents.
The court said it was "questionable whether one could be confident of eliminating all factors which would motivate and encourage liars, such as Mr Bowden, so as to justify a belief beyond all reasonable doubt in any evidence given by him".
After yesterday's decision Ward (37) was surrounded by friends and family, including his five sisters, who wept and hugged him.
As he was escorted away by prison officers, he said he had felt he would be proved innocent and was happy with the court's decision.
In November 1998 the Special Criminal Court convicted Ward of the murder of Ms Guerin at Naas Road, Clondalkin, on June 26th, 1996.
The prosecution contended that Ward participated in the planning of the murder, and his role was to dispose of the gun and motorcycle used by the killers.
This case was based on the testimony of Bowden and verbal statements allegedly made by Ward to gardaí. Ward denied any admissions.
The Special Criminal Court ruled the statements inadmissible. It said that, if they were made, about which the court expressed some doubt, they were induced by grievous psychological pressure following visits by his elderly mother and girlfriend.
That meant the prosecution case relied on Bowden's evidence.
Giving the judgment, Mr Justice Murphy, with Mr Justice O Caoimh and Mr Justice McKechnie, said the Special Criminal Court had unequivocally found, and Bowden himself admitted, that he was an inveterate liar.
Cross-examination had also exposed errors and inaccuracies in Bowden's evidence against Ward, and Bowden's credibility was further compromised as he was an accomplice in the murder.
But Bowden was much more than an accomplice, he was a witness who was given immunity for a murder to which he had in effect confessed, and he and his family were given the benefit of a Witness Protection Programme.
The law had always recognised that the evidence of an accomplice - even one who appeared a credible witness - must be corroborated from alternative sources.
Alternatively, the jury or a tribunal of fact must be reminded of the dangers of convicting without corroboration.
Whether Bowden fell into the "supergrass" category, his general lack of credibility and position as a criminal negotiating with the authorities to secure advantages for himself at the expense of his former friends and criminal associates required his evidence "to be considered with the utmost care".
Bowden's evidence, the court found, did not support the Special Criminal Court's conclusion that Ward was involved in the planning of the murder or that his role was to dispose of the gun and motorcycle.