Gardaí say investigators looking into the murder of prison officer Brian Stack more than 30 years ago are satisfied they have been provided 'with all relevant information' from within the force.
It comes after the family of Mr Stack claimed "significant information" has not been passed to the Garda team investigating the killing.
The chief prison officer at Portlaoise Prison was shot in Dublin in March 1983 and died 18 months later.
It is claimed the information about the fatal shooting, which had apparently come from an IRA informant and contained details of those responsible, had been on a file in Garda headquarters since 1990.
The family suggests that another section of the force has withheld the information "in order to protect an informant who they say they have a duty of care to".
Mr Stack's son Austin is calling on the Taoiseach to demand answers from the Garda Commissioner, and to ensure the investigation team has full access to all relevant files.
Responding to the claims, An Garda Síochana said in a statement: "The investigators leading the investigation relating to the death of Mr Brian Stack are satisfied that they have been provided with all the relevant information they require from within An Garda Síochána. The investigation team is receiving the co-operation of all relevant sections within An Garda Síochána in order to pursue all possible lines of enquiry.
"An Garda Síochána maintains regular contact with the Stack family for the purpose of keeping them informed of any relevant developments in this investigation."
It adds that the force is determined to bring the investigation to a 'successful conclusion'.
Austin Stack. Photo: Sam Boal/Rollingnews.ie
According to Austin Stack, the existence of the 'significant information' was finally acknowledged by the force in March last year, despite previous denials.
However, he believes the information has still not been passed on to the team looking into his father's death.
He told Newstalk Breakfast: "From what I can understand, the investigation team has been utterly frustrated in their attempts to retrieve this information from the other section of An Garda Síochana.
"We have worked with gardaí in that 12 month period to try and give them a chance. It's quite difficult for us to come to the media on this - but we have tried to give the gardaí the chance to get this information, and to work with the information that they have."