GARDAI are now satisfied that a faction of the Real IRA was behind the murder of former Sinn Fein administrator-turned-spy Denis Donaldson.
Officers believe that he was shot dead by Derry-based Real IRA dissidents in a bid to create problems for the mainstream Provisional republican movement, which was initially blamed for the attack.
Gardai are following a number of lines of inquiry that have emerged in recent weeks.
But a senior officer admitted last night that they did not know yet if these could lead to a breakthrough in the case.
Donaldson (56) was shot four times, in the chest, face, arm and hand, in his remote cottage at Cloghercor, near Doochary, Co Donegal, on April 4, 2007. Gardai said the investigation into his death remained 'live' and a dedicated team of detectives was working full-time on solving the case.
Suspicions about the involvement of Donaldson's former Provisional colleagues in his death circulated on both sides of the Border for a couple of years after the attack.
But as the investigation unfolded, gardai became more convinced, from emerging information, that dissidents were responsible.
They now believe that associates of a major Real IRA figure in Derry city organised and carried out the shooting.
The dissident figure has been accused of masterminding a terrorist campaign in the north-west of the island for much of the last decade and sided with the Real IRA group opposed to the group's jailed chief of staff, Michael McKevitt, when the organisation split.
One of the group was found dead at his home in Stamullen, Co Meath, last week. Seamus McGreevy (56) was awaiting extradition to Lithuania on a European arrest warrant in connection with an alleged plot to purchase arms and explosives for the Real IRA.
He was part-owner of a house in Carrigans, Co Donegal, where gardai unearthed a cannabis cultivation factory last month. The house had been rented out and McGreevy was unaware of the cannabis business.
The inquest into Donaldson's death was adjourned in Letterkenny, Co Donegal, last week until August 26, at the request of the gardai, who said "technical" avenues of investigation were being pursued.
Fine Gael's justice spokesman, Charlie Flanagan, last night called on Justice Minister Dermot Ahern to take decisive steps to tackle the very serious threat posed by dissident republicans.