High profile republican Colin Duffy, 44, and a second man aged 31 have been released unconditionally, a spokeswoman for the PSNI said.
The pair were detained in Lurgan, Co Armagh, miles from where David Black was ambushed on the M1 motorway on his way to work at the top security prison near Lisburn, Co Antrim.
A third man arrested by Gardai is still being questioned in Co Leitrim.
Duffy has been cleared of murder charges on three previous occasions - the latest last January after two soldiers were shot dead outside Massereene Army barracks.
He was arrested on Friday at his home in the Kilwilkie estate, where republicans opposed to the peace process have huge support.
Two men being held in connection with the murder of prison officer David Black in County Antrim have been released without charge.
A third man arrested is still being questioned.
The funeral for murdered Northern Ireland prison officer David Black will take place on Tuesday, it was announced today.
The service will be held at Molesworth Presbyterian Church in Cookstown.
Mr Black, who had served more than 30 years' with the Prison Service was gunned down on Thursday during a high speech ambush on a motorway as he drove to work at Maghaberry high-security prison.
A third man was arrested tonight by police investigation the murder of a prison officer in Northern Ireland.
The suspect, 29, was detained in the Irish Republic by police.
Earlier, two other men including prominent dissident republican Colin Duffy were arrested in connection with David Black's murder
Mr Black, 52, was gunned down during a high speed ambush yesterday 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.
The Police Service of Northern Ireland has welcomed independent charity Crimestoppers' offer of a £10,000 reward for information leading to the arrest and conviction of those responsible for the murder of prison officer David Black.
Independent charity Crimestoppers is offering a reward of up to £10,000 for information leading to the arrest and conviction of those responsible for the murder of a prison officer in Northern Ireland.
David Black was gunned down on his way to work in a motorway ambush yesterday.
Northern Ireland's First Minister Peter Robinson has branded the dissident republican who murdered David Black as the enemies of everyone across the island of Ireland.
Mr Robinson's comments came after ministers from the Northern Ireland Executive and the Irish Republic's government discussed Mr Black's murder at a North South Ministerial Council meeting.
Detective Superintendent Keith Agnew, from the Police Service of Northern Ireland, who is leading the investigation into the murder of prison officer David Black has given the following update: