Two men have been arrested over the murder of MI5 agent Denis Donaldson.
The 55-year-old, a senior Sinn Fein official and close colleague of Gerry Adams, was shot dead at a remote cottage near Glenties, Co Donegal, in 2006 after being exposed as a British spy.
Gardai arrested two men, one aged in his 30s and the other in his 40s, on Sunday.
They were being questioned in Letterkenny Garda Station under section 30 of the Offences Against the State Act and they can he detained for 72 hours.
Dissident republican group the Real IRA claimed responsibility for killing Mr Donaldson in 2009.
One of those arrested was Gary Donnelly, a hardline republican and independent councillor in Derry and Strabane.
Mr Donnelly was arrested on Sunday after he spoke at a centenary commemoration of the Meenbanad ambush in Co Donegal where two republicans were freed from a British Army escort in what is considered one of the first acts in Ireland's War of Independence.
Micheal Cholm Mac Giolla Easpaig, an independent councillor in Donegal who organised the event, said: "We believe Gary Donnelly's arrest to be politically motivated.
"It was a staged arrest, politically motivated and it was to undermine the work of independent councillors like ourselves."
Mr Mac Giolla Easpaig said the arrest warrant had been issued on November 22 and that Mr Donnelly was a frequent visitor to Donegal and could have been arrested on a number of occasions in the last two months.
Ciaran Shiels, solicitor for the Donaldson family, from law firm Madden and Finucane, said: "The family have no comment in relation to either arrest at this stage.
"However, we don't believe either individual to be 'Lenny', Denis Donaldson's PSNI and RUC handler.
"The family believe he is the person with the most serious questions to answer in this matter and we would urge, yet again, that the authorities speak to him under caution and as a suspect in this case."