The decision to order a retrial in the case of Mr Colm Murphy, who was sentenced to 14-years over his alleged role in the Omagh bombing, has drawn criticism of the gardaí.
The father of one of those killed in the atrocity said there should be a public inquiry after the Court of Criminal Appeal found the conviction unsafe because the judges had said two detectives had been "guilty of patent falsification" when they altered interview notes.
The three-judge panel also found that the non-jury Special Criminal Court had erred in that "a significant element in the Court's decision to convict" was based on Mr Murphy's previous convictions.
Mr Michael Gallagher, whose son Aidan was among the 29 people killed, including a mother pregnant with twins, in the 1998 bombing, said the families of the victims were "shocked and disappointed".
"We were always aware that you're at the mercy of the courts in situations like this but we never expected this result.
"Here we are six-and-a-half years on and the only person convicted has won his appeal so not one person has now been held accountable," Mr Gallagher said.
"Now we have to go through a retrial and face all that again, it is very difficult for all of us. There must be questions that the court service, the Government and the gardaí have to answer," he said.
"It seems only a full public cross-border public inquiry will uncover the truth."
The Minister for Justice, Mr McDowell said he will study the decision but could not comment further because a retrial had been ordered and the two detectives are facing criminal proceedings relating to their conduct in the case.
During the trial in 2002, Mr Justice Barr said Det Garda Liam Donnelly and Det Garda John Fahy, who interviewed Mr Murphy at Monaghan Garda Station on February 22nd 1999, had altered one of his statements, had "persistently lied on oath" at the trial and were consequently "discredited witnesses".
Labour justice spokesperson, Mr Joe Costello, said the appeal court's decision was not surprising.
"The criticisms of the conduct of a number of gardaí by the judges at the original trial in the Special Criminal Court were among the most serious ever to have been levelled against members of the force and raised very serious questions about aspects of the Garda case," he said.
He urged the Government to provide any possible assistance to the families of the victims who are pursuing a civil action against a number of people they believe carried out the bombing.