Leading Derry dissident republican Gary Donnelly who had been held by the Gardai in Monaghan in connection with the death of Denis Donaldson has been released without charge.
Mr. Donnelly was arrested in County Monaghan on Saturday as he made his way back to Derry from Dublin.
It is believed he was questioned about the 2006 killing of Mr. Donaldson.
Denis Donaldson had been a prominent member of Sinn Fein for more than twenty years and in 2006 had admitted he was a British informer.
Following this he moved out of Belfast and several months later he was shot dead at a remote cottage in the Glenties area of County Donegal.
No one claimed responsibility for the shooting at the time but later the Real IRA said they had carried out the attack.
Despite a widespread investigation by the Gardai no one has ever been made amenable for the killing. Earlier this year two men were arrested in connection with the shooting but they were later released.
Gardai had until Monday afternoon to question Gary Donnelly and then they would have had to release him or apply for an extension.
Gary Donnelly is prominent in the 32 County Sovereignty Movement and has run for election