The family of murdered IRA spy Denis Donaldson have launched legal proceedings against the Irish State over ongoing delays in holding an inquest.
The development emerged after another adjournment in the long-stalled coroner's probe into the shooting of the MI5 agent by dissident republicans 10 years ago.
Relatives of Mr Donaldson walked out of Donegal Coroners' Court on Wednesday in protest at the latest hold-up.
The 55-year-old senior Sinn Fein official and close colleague of party president Gerry Adams was shot dead at an isolated cottage near Glenties in Co Donegal in April 2006.
He had been living there since his exposure as an MI5 agent the previous year.
With the inquest approaching its 20th adjournment, Mr Donaldson's relatives have issued proceedings with the High Court in Dublin against Donegal coroner Denis McCauley; the Director of Public Prosecutions, the Garda Commissioner, the Attorney General and the Minister for Justice.
Family solicitor Ciaran Shiels said they wished to challenge the ongoing delays and the "antiquated" legislation under which the multiple adjournments had been granted.
After the hearing in Letterkenny, Mr Shiels said: "There comes a point after so many adjournments, after the tenth anniversary, that the delay in commencing the inquest proper becomes intolerable.
"With that in mind the family instructed me to commence judicial review proceedings against the Garda Commissioner, the coroner, the Attorney General, the DPP and also the Minister of Justice."
He added: "Today the family have walked out of the inquest and I have been instructed not to attend further until there is definitive ruling from the courts in the south."
Last year, the family launched separate legal proceeding with the courts in Europe over the delays in the investigation.
Dissident republican group the Real IRA claimed responsibility for the murder in 2008 but the circumstances surrounding Mr Donaldson's outing as a British agent and subsequent assassination have been shrouded in mystery.
The Garda believes the killers can still be caught and do not want an inquest to proceed while its criminal investigation remains live.
In 2014, gardaí made a mutual assistance request to a police force outside the Irish Republic in a bid to gain potentially "significant" material.
Today, Garda Superintendent Michael Finan told Mr McCauley his officers had obtained that material last month.
He asked for an adjournment of four months to enable detectives to pursue enquiries linked to the fresh evidence.
"I regret the number of adjournments but the investigation into the death of Mr Donaldson must be allowed to gain all available evidence and present it to the DPP," he said.
Mr Shiels said the family did not accept the "bona fides" of the application.
Relatives of Mr Donaldson have long been critical of the Gardaí's handling of the investigation.
Specifically they have accused gardaí of refusing to hand over a journal Mr Donaldson was writing in the months before his death to Police Ombudsman investigators in Northern Ireland, and of failing to interview the police handler who worked with the Sinn Féin official.
Counsel for the state Stephen Byrne insisted there was no suggestion the application for adjournment was anything other than genuine.
"There is no evidence or no concrete evidence to support such an insinuation," he told the court, which was sitting in the Mount Errigal Hotel.
Granting the adjournment to August 31, Mr McCauley said he was satisfied there continued to be "momentum" in the criminal investigation.
"The momentum that has been developing would appear to be continuing to be moving forward," he said.