Police have arrested two men in Derry and a third in Belfast in connection with the theft of sensitive intelligence documents from the Special Branch's Castlereagh headquarters in Belfast on St Patrick's night. Gardaí also searched a caravan in Co Donegal belonging to one of the men.
Mr Raymond McCartney, a senior republican and former prisoner, and his brother Andrew were arrested at their homes yesterday.
Mr McCartney, a married man with a five-year-old son, is a prominent republican in Derry.
His arrest has greatly angered Sinn Féin, but police sources say the arrest would not have been made unless justified.
He served a lengthy sentence in the Maze prison for the murders of a Special Branch officer, Mr Patrick McNulty, on January 27th, 1977, and of an industrialist, Mr Jeffrey Agate, six days later.
During his time in prison, Mr McCartney became the IRA's OC (Officer Commanding) and played a leading role in the dirty protests and in the first hunger strike in 1980.
He was arrested at his Fernabbey Close home after police officers using sledgehammers had forced their way into the house. During the search, the police removed several items including videos and papers.
At the same time, the home of Mr McCartney's brother, Andrew, was also searched two miles away in The Branch, where documents, computer discs and videos were removed by the police. The offices of the Derry Taxi Association, of which Mr Andrew McCartney is manager, were also searched.
The search of Mr Andrew McCartney's caravan, at Tullagh Bay, near Clonmany, took place early yesterday morning as PSNI officers were searching three premises across the Border in Derry.
Following the arrests of the McCartney brothers, Sinn Féin organised two street protests in the centre of Derry, one at Shipquay Street and the other at Queen's Quay, both of which passed off peacefully.
A Sinn Féin Assembly member, Ms Mary Nelis, whose daughter Kathy's home was searched in a similar operation in Derry last Saturday, condemned the arrests.
"It is just a clumsy attempt to deflect the attention of the various inquiries into the Castlereagh incident onto republicans. If this is the new policing, God help us," she said.
The Sinn Féin chairman, Mr Mitchel McLaughlin, also condemned the police operations.
"These actions are completely unacceptable and must end. The PSNI Special Branch cover-up into the raid on Castlereagh is now in full swing. But people will not be fooled and republicans will not be scapegoated."
Six people were arrested over the Easter weekend. Five were released and one, Mr John O'Hagan, a republican, was charged with possessing material useful to terrorists. The charges are unconnected to the Castlereagh robbery.
Police officers have also travelled to New York to interview a former Castlereagh worker.
The FBI has already questioned the suspect.