Taoiseach Micheál Martin has told the Dáil that he will pursue both the British and Northern Irish authorities regarding the no-warning car-bomb attack on Belturbet, Co Cavan, in which two teenage civilians were murdered in 1972.
Loyalist paramilitaries were responsible for the bombing which killed Geraldine O'Reilly, 15, and Paddy Stanley, 16. However there have also been allegations of collusion by British security forces in the attack.
Mr Martin told the Dáil that he would pursue the matter "with the British authorities and the authorities in Northern Ireland" because the families involved have been "left with no answers" or closure.
He described the bombing attack on Belturbet Main Street as "heinous" and declared that he would "do what I possibly can" to get answers for the families.
He told the Fianna Fáil TD for Cavan-Monaghan, Brendan Smith, that the garda investigation into the killings was "still an open investigation."
Mr Smith also described the attack as a "heinous crime".
He told the Dáil that the attack emanated from Co Fermanagh but, he asserted "there has never been a proper or thorough investigation" by the authorities in Northern Ireland into what happened.
Mr Smith said he presented new evidence to the Dáil last September regarding collusion between the British state forces and loyalist paramilitaries regarding bombings in border counties in the south.
He said this information came from research by the University of Nottingham.
Deputy Smith said: "The least these families - the O'Reilly and Stanley familes - deserve is the truth."
His constituency colleague, deputy Niamh Smyth, said that RTE Investigates programme last night into the attacks showed the "horror, trauma and the tragedy of the case."
She said it was "utterly wrong" that, 48 years after the attack, the families had not seen the Garda files into the bomb-attack because their investigation was deemed to be live.
Deputy Smyth called for a "proper and full investigation into this atrocity."
In the RTE Investigates programme, it was revealed that a military commander of British Army forces in west Fermanagh admitted to co-operating with loyalist paramilitaries in the 1972 bombing of a bridge spanning the border between Co Cavan and Co Fermanagh.
The Aghalane Bridge had been used by IRA units in a series of 1972 raids into south Fermanagh that targeted security forces, particularly local members of the Ulster Defence Regiment.
In a 2005 oral history interview with the Imperial War Museum, Retired Major Vernon Rees described being approached by Jack Leahy, a unionist councillor from Lisnaskea.
Amid increasing unionist fears about weak security along the southern side of the border, Mr Leahy intimated that loyalist paramilitaries wanted to blow up the bridge.
According to Major Rees' account on the recording, which was obtained by RTÉ Investigates, Mr Leahy asked him if he would "feel better if that bridge wasn't there".
"Yeah, of course I would, but there is no way we can do anything about that," Major Rees recalled saying in reply.
Mr Leahy suggested that Major Rees keep his soldiers away from patrolling the bridge for four hours.
Major Rees said in the 2005 interview that he found himself contemplating whether he should "co-operate ... in the destruction of a main road in the United Kingdom."
While British security forces, the Royal Ulster Constabulary and the Northern Ireland Office had concluded that a closure of the bridge could alleviate security concerns, the Irish state was not prepared to shut down an approved road that served as the main route between Dublin and Co Donegal via Enniskillen.
Tensions in the area escalated in September 1972 following the IRA farmhouse murder of UDR member Tom Bullock and his wife, Emily.
"I thought it would be wonderful if that bridge was down," Major Rees recalled thinking. "So I leaked it through the Special Branch again that there would be no soldiers on that bridge between eight o'clock ... and midnight."
At the agreed time, loyalist paramilitaries placed an explosive charge on the old stone bridge.
Following the blast, Major Rees, who was then a Captain in the British Army, examined the bridge and found the gang had failed to disable it.
Rather than round up those who caused the explosion Major Rees ordered a munitions expert from his own unit to finish off the job.
Major Rees said that destroying the bridge "saved dozens of lives".
Against strong opposition from unionist-dominated Fermanagh County Council, Cavan County Council moved to repair the bridge and restore direct links between Dublin and Co Donegal.
On 24 December 1972, cross-border traffic returned to Aghalane, using a temporary bailey bridge installed by Irish Army engineers.
Just four days later, loyalist paramilitaries drove a car bomb across the bridge to Belturbet in Co Cavan, detonating it on Main Street without any warning.