The family of a senior Irish prison officer murdered by the IRA has received a state apology on Wednesday for failings in investigations into his killing.

Brian Stack, a father of three, was crossing a street in Dublin, after leaving a boxing match in 1983, when he was shot in the back of the neck.

Stack, who was the chief prison officer at the high-security Portlaoise Prison, was left paralysed and died 18 months later, aged 49.

There were three separate garda (Irish police) investigations into Stack's death, but no-one was brought to justice for his killing.

Taoiseach (Irish prime minister) Micheál Martin offered an apology on behalf of the state during a sitting of the Dáil (Irish parliament).

Stack's wife Sheila and her sons Austin, Kieran and Oliver were in the Dáil chamber for the apology.

Martin said the Provisional IRA is "still in the possession of all the facts" on this case.

Speaking to BBC Radio Ulster's Good Morning Ulster programme Brian Stack's son, Austin Stack, said the apology "means an awful lot to us".

"It's a great sense of comfort, to particularly my mother and to myself and my two brothers, because the state is officially owning up to the errors and the missions that happened," he said.

He went on to say that the serious crime review team looked into the first investigation and "they found 194 errors and omissions".

"So I have, and my family have, met with several ministers for justice down through the years and we have a requested sight of that report.

"And every time we've requested it, we've been told that it's an internally valid document and that we cannot see it." Austin Stack said that Wednesday would be a very emotional day for his family.

"My dad was doing a very difficult job at a very difficult time in our history," he said.

"He was awarded the Irish Prison Service's highest bravery award for that work that he was doing. And this is further vindication of him and his good name." Prior to the Dáil proceedings, the Stack family held a private meeting at government buildings with the taoiseach and Minister for Justice Jim O'Callaghan.

In 2007 the Garda Commissioner directed a review of the case by the Garda Serious Crime Review Team. Over 200 recommendations were made relating to the cases.

This review led to "serious failings" being found as well as "the shortcomings in the management" of the earlier Garda investigation.

These failures, listed by Martin in the Dáil, are: failure to keep a map made of the crime scene, a failure to keep a motorbike helmet found near the crime scene and linked to the crime, a failure to keep custody of material exhibits, including various fingerprints, samples and debris gathered during the investigation.

The taoiseach also said there was a failure to document some potentially important aspects of the original investigation, including whether Brian's colleagues at Portlaoise Prison were interviewed and whether prisoners at the prison were interviewed.

There was also a failure to interview the Stack family and to interview Brian's wider group of friends.

"It is plainly and utterly unacceptable that material that was potentially of evidential value to the investigation can no longer be located by An Garda Síochána.

"It is admitted by An Garda Síochána that these are serious matters that had an impact on the investigation," Martin said.

"As Taoiseach, and on behalf of the Government, I want to formally apologise to the Stack family for these failings." Speaking in the Commons during Northern Ireland questions on Wednesday, Secretary of State Sir Chris Bryant said he "warmly welcomed" the taoiseach making the apology.

Asked about the matter by Democratic Unionist Party leader Gavin Robinson, Sir Chris said Dublin doing so was "entirely right and proper" and went to the heart of discussions MPs had been having this week as they debated the government's Troubles legacy bill He added that it was "incumbent on all of us to make fulsome and not mealy-mouthed apologies".

The IRA admitted killing Stack in 2013 after his family mounted a long campaign to secure the admission, and met Sinn Féin's Gerry Adams and a former IRA commander. Adams, at that time, expressed his "regret" to the Stack family over the killing.

A Sinn Féin spokesperson said that "in a 2013 statement, a former IRA leader acknowledged that IRA volunteers were responsible for Brian Stack's killing".

"The statement said the shooting had not been authorised by the IRA leadership, accepted IRA responsibility for his death, said it should not have happened and expressed sorrow for the pain and hurt suffered by the family."

The spokesperson added: "As republicans, we acknowledge the hurt caused by republican actions. That suffering cannot be disowned. We are sorry for all the lives lost during the period of conflict on this island, without exception."

Irish foreign affairs minister Helen McEntee also spoke during the State apology, she said: "The State failed you during their investigation into Brian's killing." She said Brian was "targeted" by the Provisional IRA and said "they are responsible".

"To Sheila and to all of the Stack family, we are deeply sorry for all that you have endured, for the failures of the investigation and the additional suffering they have caused you, we are deeply sorry. I hope today's formal apology brings some measure of peace and comfort." Donegal Sinn Féin TD (member of Irish parliament) Pearse Doherty said the Stack's family "long search for answers deserves respect".

"No apology can restore Brian Stack's life or return the years spent seeking answers but it can recognise the wrong done." He said the failures of the garda investigation "compounded" the suffering of the Stack family.

In 2019, the family received an apology from then garda commissioner Drew Harris in relation to the handling of the investigation into the murder.

In 2023, gardaí told the family that the file on the case - which was with the DPP (Director of Public Prosecutions) - was being sent back to police for further investigation.

Stack was the only prisoner officer in the state killed by violence related to the Troubles in Northern Ireland.