Two men arrested over the murder of IRA informer Denis Donaldson remain in custody.
A 31-year-old suspect was detained just hours after a 69-year-old man was held for questioning yesterday evening.
Both men are being held at Letterkenny garda station, Co Donegal, under Section 30 of the Offences Against the State Act and can be held for up to 72 hours.
The pensioner, originally from the Dungloe area of the county, was detained on suspicion of withholding information about the killing.
It is understood he had been living in Glasgow for the last six months.
The younger man, from Annagry, Co Donegal, was detained on suspicion of possession of firearms on the day of Mr Donaldson’s killing.
The former senior Sinn Fein officer, from west Belfast, was shot dead at a remote cottage in Co Donegal on April 4, 2006.
No-one has been charged in relation to the 56-year-old’s murder and the arrest is understood to be the first by gardaí.
A senior officer described the case as “complex”.
Just months before his death, Mr Donaldson publicly revealed that he had been working as an informer inside the republican movement for years.
Only last week, his family demanded that both the Garda and PSNI do more to bring his killers to justice.
In a statement issued through solicitors, they claimed that British security agencies had a part to play in his death.
In October 2002 Mr Donaldson was arrested after police raided Sinn Féin’s offices at Stormont, where he worked as the party’s head of administration, as part of an investigation into republican intelligence-gathering.
His arrest, along with two other men, became known as Stormontgate – a republican spy ring at the heart of government.
The controversy caused the collapse of the devolved power-sharing administration in the North.
But in December 2005 the charges against the three men were dropped.
Days later Mr Donaldson was expelled from Sinn Féin after admitting he had been a paid British spy for 20 years. He moved to Cloghercor, Doochary, near Glenties in Co Donegal.