The family of a senior prison officer who was murdered by the Provisional IRA in early 1980s has called on the Garda to explain the failings in its original investigation into the killing.

Brian Stack, then chief officer of Portlaoise Prison, was shot outside the national boxing stadium in Dublin on March 25th, 1983. He died from his injuries 18 months later.

Austin Stack, one of Brian Stack’s three sons, said the family had achieved an “element of closure” after the IRA admitted for the first time that its members carried out the killing. However, he said the Garda has never provided an adequate explanation for the shortcomings in its inquiries into the killing.

While the investigation was initiated at Kevin Street station in Dublin, he questioned why it went no further Newland’s Cross on the outskirts of the city and never pursued inquiries at Portlaoise prison itself.

“It appears to the Stack family that the original investigation was seriously compromised from the outset - a damning indictment for what at the time a capital murder charge case, the most serious criminal charge in the State,” Mr Stack told reporters outside Leinster House this afternoon. “Brian Stack was a proud and loyal servant of this State, a role model in his community and a dedicated family man.”

He called on Garda Commissioner Martin Callinan to meet the family to provide it with an update on the current investigation into the murder.

A Garda spokesman declined to respond to the family’s statement. “A detective superintendent has been appointed to investigate and liaise with the family. The investigation and liaison is ongoing and it would be inappropriate to comment further at this stage.”

In a statement to the Stack family early last week, the IRA said its members were acting on orders when they carried out the attack. However, the statement said the attack was not authorised by the leadership of the parliamentary organisation. “Some years later, when the Army Council discovered that its volunteers had shot prison officer Brian Stack, the volunteer responsible for the instruction was disciplined,” the IRA statement said.

Speaking alongside his brother Oliver outside Leinster House this afternoon, Austin Stack told how the family members received the statement last week from a former senior IRA leader at a meeting with Sinn Fein leader Gerry Adams.

He and his brother were driven in a blacked-out van to an undisclosed location off the M1 motorway near Dundalk. The ex-IRA leader read the statement to them over a table in the private one-storey house, before asking them to transcribe it for themselves.

Austin Stack said the meeting, over tea and biscuits, followed a series of talks between the family and Mr Adams. He thanked Mr Adams but said the family was still left with unanswered questions.

“In particular, who are the individual IRA members responsible for the murder of chief officer Brian Stack and why does it appear the original Garda investigation was compromised from the outset?”

Austin Stack said he believes he knows who ordered the killing and believes the people who carried it out were from the IRA organisation from the Republic. The person responsible is still alive, he said.

“I still want to meet face-to-face with my father’s killer,” he said. “I would sit down with him and the first thing I would do, like I did with Gerry Adams, I would explain the effect this had on our family, the effect it had on us.

“I would ask him why he did it, how he feels now at this stage 30 years later, does he have a conscience, does he sleep well at night, those are the sort of questions I would ask him.

“I would actually sit down and have an open, frank discussion with him.”

The IRA statement said: “Prison officers were killed by the IRA in the north. These killings were sanctioned by the IRA leadership but none were sanctioned in the south and none was asked for in the case of your father.”

It continues: “In Portlaoise a brutal prison regime saw prisoners and their families suffer greatly. This is the context in which IRA volunteers shot your father.

“This action was not authorised by the IRA leadership and for this reason the IRA denied any involvement. Some years later, when the Army Council discovered that its volunteers had shot Prison Officer Brian Stack, the volunteer responsible for the instruction was disciplined.

“This operation should not have taken place,” it states. “While the IRA can no longer comment on this matter let me express my sorrow for the pain and hurt your family suffered.”

In a statement today, Mr Adams said the family had asked for his assistance “in seeking answers and closure to questions they have surrounding the killing of their father”.

He added: “On behalf of Sinn Féin I extend my regret at the killing of Brian.

“I hope that these recent developments will help them achieve the closure they have sought for 30 years.”

Mr Adams said that addressing “complex and painful legacy issues” was an “enormous challenge”.