By Kevin Connolly BBC Ireland correspondent

The murder of Veronica Guerin in 1996 caused shock waves which still reverberate through Irish society to this day.

In part, it was the brutality of the way she was killed - shot repeatedly at the wheel of her car on a busy road in broad daylight by the pillion passenger of a motorbike which pulled up alongside her at traffic lights.

In part though it was also the knowledge her crusading investigative journalism had exposed a corrupt, extensive and violent world of organised crime in Ireland.

The drug-dealing gangsters whose crimes she chronicled and whose lifestyles she exposed hated and feared her enough to threaten and finally to kill her.

As the Irish parliament was recalled to consider the implications of the killing - which changed people's perceptions of the nature of the society in which they lived - the largest man-hunt in the history of the state began.

Authorities who relied on turning criminals against each other for testimony may be forced to use new tactics

The way the Irish police set about securing convictions though has helped to ensure the case has had far-reaching implications for Ireland's system of justice, as well as for the family Veronica Guerin left behind.

The investigation centred on the criminal gang led by John Gilligan, a drug dealer who liked to live like a country gentleman but who had also beaten Guerin up as a brutal warning to keep out of his affairs.

Gilligan was eventually acquitted of her murder after a lengthy trial at Dublin's Special Criminal Court, but sentenced to a total of 28 years in prison for drugs offences.

Raising doubts

Police did achieve convictions for murder against two members of the Gilligan gang, Paul Ward and Brian Meehan, but only by cutting deals with two other members, Charles Bowden and Russell Warren.

Guerin: Her murder triggered a huge outcry

Ward's appeal against conviction relied on raising doubts about the quality of evidence provided in circumstances where investigating officers or prosecuting authorities have offered incentives of some kind to one criminal to testify against another.

That may well mean there will be similar appeals against other convictions in the case to come, even though Paul Ward won't be freed from prison immediately because he's also serving a 12-year sentence for his part in a prison riot while he was awaiting trial.

There was a huge public outcry when Veronica Guerin was murdered, a demand for the killers to be brought to justice that placed enormous pressure on police and politicians alike.

If the convictions achieved so far are overturned, that public anger may well be felt again, and the authorities who relied on turning criminals against each other for testimony may be forced to turn to new tactics.