A third man has been arrested by police probing the murder of a prison officer in Northern Ireland.
The suspect, 29, was detained in the Irish Republic by police. Two other men including prominent dissident republican Colin Duffy were earlier arrested north of the border.
David Black, 52, was gunned down during a high speed ambush on a motorway as he drove to work at Maghaberry high security prison. His killing has prompted condemnation from across Britain and Ireland and police have blamed it on dissident republicans.
Irish police confirmed: "Gardai have arrested a 29-year-old man in Co Leitrim this evening in connection with the murder of 52-year-old David Black in Co Armagh yesterday morning. The man is detained in Carrick-On-Shannon Garda Station under Section 30 Offences Against the State Act 1939."
Duffy was detained with a second man in Lurgan, Co Armagh, just miles from where Mr Black was ambushed on the M1 motorway on his way to work at the top security prison, near Lisburn, Co Antrim.
Detectives leading the inquiry insisted they needed the public's help to bring the killers to justice. Superintendent Keith Agnew declared: "Condemnation, however strident, is not enough. It needs to be translated into information if our investigation is to make maximum progress."
Duffy, 44, who has been cleared of murder charges on three separate previous occasions - the latest last January after two soldiers were shot dead outside Massereene Army barracks in March 2009 - was arrested at his home in the Kilwilkie estate where republicans opposed to the peace process have huge support.
Politicians on all sides condemned the murder of the prison officer, who was planning to retire next year after more than 30 years of service.
Enda Kenny, the Irish Republic's Prime Minister who was in Armagh for talks with Northern Ireland First Minister Peter Robinson and Deputy First Minister Martin McGuinness, said the dissident republicans had been linked to criminality and drug dealing which had also led to deaths on the streets of Dublin.
Mr Black's murder had overshadowed the meeting, he said. He added: "We do not want to see a return to this, nobody on this island wants to see a return to this."
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