It's been confirmed that two men are now being questioned by garda about the murder of Dennis Donaldson near Glenties in 2006.
One of them is Independent Derry City and Strabane district councillor Gary Donnelly.
Cllr Donnelly, who is 46, was attending a commemoration in Meenbanad yesterday when he was arrested and taken to Letterkenny Garda Station for questioning.
This morning, gardai confirmed that a second man in his thirties has been detained, and is also being questioned in Letterkenny.
Gardai are appealing to anyone with information about the murder of Dennis Donaldson to contact the incident room in Letterkenny, or any Garda station.
Dennis Donaldson, a former Sinn Fein member, was shot dead in April 2006 in a remote cottage outside Glenties. His killing came four months after he confessed to working as a British agent for police and MI5 for 20 years.
Gary Donnelly was previously arrested and questioned in connection with the Donaldson Killing in September 2011, he was released without charge.