Suspected IRA members’ involvement in a ruthless killing threatens to create a political backlash and casts a new spotlight on the actions of republicans.
In July 2005 the organisation promised to put its weapons beyond use and decommissioned them.
A body which monitored the ceasefire for the British and Irish governments later declared the IRA had disbanded.
But police have said members of the Provisional IRA may be involved in the shooting dead of Kevin McGuigan in Belfast recently.
Several arrests had been made, and among those questioned by police was Sean Kelly, the surviving Shankill Bomber (Mr Kelly has not been charged with any crime in connection to this case).
Nationalist SDLP leader Dr Alasdair McDonnell said: “The Provisional IRA in whatever form it exists, despite whatever contortions it may have gone through, still appears to claim the right to exercise life and death decisions over anyone in the community that they develop a grudge against.”
Mr McGuigan was suspected by some in the republican movement of involvement in the murder of former IRA leader Gerard “Jock” Davison in the nearby Markets area of Belfast three months ago.
Mr Davison and Mr McGuigan were at one time involved in Direct Action Against Drugs.
It was a vigilante group which claimed responsibility for the killing of more than a dozen alleged drug dealers from the 1990s to the early 2000s.
Police are investigating whether a criminal group calling itself “Action Against Drugs” was behind Mr McGuigan’s killing.
Earlier this year Mr Davison was shot dead in Belfast after he was linked to a pub fight which produced one of the most notorious murders in Northern Ireland’s recent history.
The killing of Robert McCartney, 33, following a brawl at Magennis’s Bar in the city centre in January 2005, was alleged to have been carried out by members of an IRA which was to decommission all its arms later that year.
Mr Davison was among three Provisionals expelled following an internal investigation by the organisation after the death of the father-of-two.
He was questioned by police but released without charge.
Mr McCartney’s sisters blamed the IRA for murdering him and accused the organisation of interfering with witnesses. They took their fight for justice to the White House, meeting President George W Bush on St Patrick’s Day in 2005. Nobody has been convicted of killing their brother.
Initially, Sinn Fein rejected claims that IRA members were present.
The killing came at a delicate time for the party, which was involved in negotiations aimed at securing its support for the police.
The process had already been threatened by a late 2004 raid, blamed by police on the IRA, when an armed gang stole £26.5 million from the Northern Bank in Belfast city centre.
At the end of 2005 the case against Denis Donaldson, at the centre of an alleged IRA spying incident at Stormont, was dropped. Days later it emerged the former head of Sinn Fein’s Stormont administration office was a paid security force agent and he was shot dead in Co Donegal in April 2006.
In October 2007, Paul Quinn, 21, from Cullyhanna in South Armagh, died after being attacked and beaten at a shed near Castleblayney in the Republic of Ireland.
His family have blamed members of the IRA – but Sinn Fein have denied this.