BELFAST (Reuters) - Two men arrested by police in Northern Ireland hunting for those responsible for the murder of a prison officer who was shot as he drove to work were released without charge on Sunday, police said.
According to a security source one of the men released was Colin Duffy, a prominent Irish nationalist acquitted earlier this year of the murder of two British soldiers.
The men were detained on Friday, a day after the prison officer, David Black, 52, was shot dead.
Black's murder was the first killing of a prison officer in Northern Ireland in almost 20 years and the fifth fatal attack on a member of the security establishment since the 1998 Good Friday peace deal.
The pact largely ended three decades of sectarian conflict in Northern Ireland between Protestants loyal to British rule and mostly Roman Catholic nationalists who want to unite with the southern Irish republic.
Police chiefs have blamed militant nationalists opposed to the peace process for the murder which has prompted condemnation from both sides of the political divide.
Black, a father of two, was shot while driving his car in County Armagh. He worked at the top security Maghaberry prison where militant nationalists have been protesting against their living conditions.
A third man arrested south of the Irish border in the county of Leitrim later on Friday is still being questioned.
Life-long Irish nationalist Duffy was acquitted in January of the murder of two British soldiers shot dead outside Massereene army barracks in Antrim by the Real IRA in 2009.
He had been acquitted of murdering members of the security forces twice before.
(Reporting by Ian Graham, editing by Padraic Halpin and Christopher Wilson)