"Significant progress" has been made in the investigation into the Belturbet bombing that killed two people in 1972, Garda Commissioner Justin Kelly has said.
Speaking at a cross-border policing conference in Co Cavan, Commissioner Kelly said that gardaí had made significant progress in the investigation and opened a number of new lines of inquiry.
"That work will continue. It's difficult work, but we have to be meticulous. We have to do everything we can to try and get justice for these families," he said.
Gardai would "leave no stone unturned", he said.
A no-warning bomb exploded on the main street of the Cavan town on the 28 December 1972.
Two people were killed in the bombing, 16-year-old Patrick Stanley from Clara in Co Offaly, and 15-year-old Geraldine O'Reilly from Belturbet.
Read more:
The Belturbet bomb: an atrocity that time forgot
Gardaí reopened an investigation into the bombing almost three and a half years ago.
Commissioner Kelly said it was the first time he had answered a question on the issue of the Belturbet bombing, and he offered his condolences to the families involved.
Commissioner says information sharing on legacy issues 'complex'
The Garda Commissioner also said that cross-border sharing of information about legacy cases was "complex" and "not straight forward".
Speaking to reporters at the policing conference Commissioner Kelly said: "It's not straight forward. But of course, we do everything we can from An Garda Siochana's perspective, to make sure we have everything we need to progress that".
PSNI Chief Constable Jon Boutcher, also attending the conference, said it was "incumbent on all of us" to make sure families got the information they deserve.
"That means the passing of information from whatever jurisdiction the information is held that is relevant to those investigations".
Mr Boutcher said he believed there were still "impediments in place" in legacy legislation regarding information.
He said: "I've been very clear about new legislation, that I think there are impediments in place about unfettered access to information, so we're not there yet.
"But from a PSNI perspective, as the Chief Constable, if An Garda Siochana require information from us, they will be provided with it."
Minister for Justice Jim O'Callaghan said he would be publishing a general scheme of new legacy legislation in May and hopes it will be enacted "by the end of the year".
Last year, both governments agreed a joint framework on legacy.
Minister O'Callaghan said he recently met with Secretary of State for Northern Ireland Hilary Benn, who provided an update on the British side of the legislation that is to be introduced in the House of Commons.
The minister said the Irish legislation was "very much dependent on when and how that legislation is enacted in the UK, because it has to mirror the UK legislation".
"Both governments are committed to ensuring legislation is put in place to ensure Troubles related killings can be investigated in order to try to provide some answers to families," he said.
In January, the Garda Troubles Legacy Liaison Unit was set up to act as a single point of contact for co-operation with the Legacy Commission, once it is established.
The unit itself does not carry out investigations but acts as a point of contact for victims and families about the garda investigations into Troubles-related cases in this jurisdiction.
