Sinn Féin leader Gerry Adams has said that the son of a prison officer who was killed by the IRA over 30 years ago gave the names of suspects to him.
Brian Stack, who was a chief officer in Portlaoise, died 18 months after he was shot in the back of the neck in 1983.
Mr Adams named four senior Sinn Féin figures, including two current public representatives, in an email to the Garda Commissioner in February of this year.
He claimed he had been given the names by Mr Stack's son, Austin, and that he was forwarding on the names "to remove any uncertainty about this".
However, Austin Stack today accused Mr Adams of being "untruthful in the extreme".
He said at no stage did he reveal any information that he had to Mr Adams "despite him asking".
He also said his brother Oliver "was present and witnessed this conversation".
Mr Adams is currently in Cuba for the funeral of Fidel Castro.
He issued a statement this evening saying that he met the Stack family in 2013 at their request and that during the course of their conversations he was given a number of names by Austin Stack.
Mr Adams said Austin Stack told him that he had been given the names by "journalistic and Garda sources".
He said that "Austin asked me to ask those named if they would meet with him. I did this with those I could contact. They declined to meet at that time. I told Austin Stack this".
Mr Adams said he passed on the names to the Garda Commissioner "while making clear I have no information on the death of Brian Stack".
He said the Garda is the "only body that can investigate this matter. I am prepared to co-operate with this on this."
Earlier, speaking on RTÉ's Today with Sean O'Rourke, Austin Stack said he and Oliver met with Mr Adams up to six times, but at no time did they ever discuss or give names to Mr Adams.
He said he was contacted by gardaí last week who told them they had received an email in February from Mr Adams' secretary.
Mr Stack said this email included one name that he had never discussed in connection with his father's case, and he did not "know where Gerry Adams was coming from in suggesting that."
A Sinn Féin spokesperson said: "This issue was dealt with at the time of the election. Gerry Adams made clear that he had received these allegations from Austin Stack.
"Mr Adams subsequently passed on Mr Stack's allegations to the gardaí. Any investigation is a matter for An Garda Síochána."
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The matter was raised during Leaders' Questions in the Dáil this afternoon, with Fianna Fáil leader Micheál Martin describing it as an extraordinary situation.
Taoiseach Enda Kenny said that the "family deserve to know the truth" and called on Sinn Féin to address the "contradiction".
