The murder of Veronica Guerin prompted the introduction of a protected witness programme allowing for accomplices to turn "State's evidence". This meant they could be given some immunity from prosecution, money, new locations and identities in return for giving evidence against those involved in serious crime.
This policy was pursued in the investigation of the murder, where certain members of the Gilligan gang were persuaded to give evidence against others, including its leader. Two gang members, Paul Ward and Brian Meehan, are already serving life sentences for the murder based on this evidence.
The fact that the Special Criminal Court decided not to bring in a guilty verdict against John Gilligan on the murder charge means accomplice evidence cannot be relied on by the prosecution without corroboration. The use of such uncorroborated evidence in Northern Ireland was abandoned when a number of convictions based on it were overturned.
The trial of Gilligan differed from that of Ward, also convicted of the Guerin murder, in that the only evidence against Gilligan was that of accomplices on the protected witness programme, Charles Bowden and Russell Warren. They have not been prosecuted for their role in the murder, though they are serving sentences for drug offences.
In the Ward case, the prosecution produced a statement in which he confessed to being an accessory to the murder. This statement was contested during the trial, and implicitly rejected by the court, which made stinging criticisms of the conduct of the Garda in its judgment.
This left the evidence of Bowden. The court accepted that Ward corroborated much of what Bowden had said about the involvement of both of them in the gang. It then extended that belief to his evidence of Ward's involvement in the murder, which Ward had denied.
There was no confession evidence in the Gilligan case and the essential evidence against him in relation to the murder charge was that given by protected witnesses Bowden and Warren.
Bowden and Warren have admitted involvement in the journalist's murder. Warren stole the motorbike used in the murder. He said he witnessed the murder from a van travelling behind and told the court he informed Gilligan about it on the phone immediately afterwards. The court did not accept this had been established beyond reasonable doubt.
Bowden has admitted cleaning and loading the gun used in the murder and said he knew Ms Guerin was going to be "shot or shot at" when doing so. He also admitted minimising his role in the murder when first questioned by gardai. He gave evidence supporting the prosecution's case that Gilligan was "in control and command" of a criminal gang, including himself, which imported large amounts of cannabis.
The court found there was corroborating evidence linking Gilligan with imported cannabis, but none linking him with the murder and firearms charges.
Prof Dermot Walsh, of the Centre for Criminal Justice in the University of Limerick, who is the author of a study of the supergrass trials in Northern Ireland, has criticised convictions based on the uncorroborated evidence of accomplices. "In the North you had evidence from people heavily involved in terrorist activity. They had a vested interest in exaggerating their evidence against individuals the authorities wanted to catch. It's the same here.
"The Court of Appeal in Northern Ireland overturned most of them and gave a very severe warning about their use in the future. The Ward case did not follow this. We should be very slow to go down that road." In Britain, he said, corroboration was required when the evidence of a protected witness was used.
During the Gilligan trial, evidence was heard of money paid to Bowden and Russell by the Garda, and of their expectations of early release. There was a suggestion that a memo from a Department of Justice official that their early release would be "dependent on their performance in court" made it contingent on the evidence they would give, though this was denied.
Had the judges of the Special Criminal Court accepted the use of uncorroborated accomplice evidence, there would have been clear implications for the future and for the trials of people less important than Gilligan. It would open the possibility that a criminal fearing prosecution for his crimes could offer evidence against an accomplice which placed the primary responsibility for the crimes on that accomplice, even if it was his. He would then enjoy a safe retirement from crime at the taxpayers' expense.
Someone would be convicted for the crime, the public would be satisfied and the accomplice would probably have been guilty of something, so he would be in no position to generate public sympathy. The Government could boast of its successes against crime.
The implications, however, for the integrity of our criminal justice system would be serious. What would it say to the communities from which most criminals come if young people dabbling in crime knew the seriousness of the offences did not matter or that they could be convicted of crimes they did not commit on the word of an accomplice?
What would it say to ambitious young gardai if they knew that the way to secure convictions was by persuading criminals, who might have been guilty of serious offences, to stitch up their pals while themselves avoiding the full rigours of the law?
The Special Criminal Court has made it clear that corroboration will be required when accomplice evidence is used. This means that such evidence has to be combined with evidence drawn from independent investigation of the crime.