The boys have been ordered from a bus and shot on the roadside in Co Armagh in January 1976 “for no different cause than they have been Protestant”, the inquest concluded.
No-one has ever been convicted in reference to the killings.
The assault had been admitted by a gaggle calling itself the South Armagh Republican Motion Drive.
However delivering his findings this afternoon, coroner Brian Sherrard outlined intensive ballistics proof linking the weapons used at Kingsmill to a sequence of assaults carried out by the IRA.
He stated: “Shortly after the assault the so-called South Armagh Republican Motion Drive claimed accountability for it. That was a lie.
“The assault was carried out by the IRA working below the authority of the Military Council which had, in April 1975, given vast authorisation to IRA items.
“It was subtle and complicated, involving a number of people in its planning and execution.”
Nonetheless, Ulster Unionist chief Doug Beattie criticised the failure to determine publicly these accountable for the bloodbath, including that the inquest “has failed at each stage”.
He known as on the Authorities “to do the precise factor” and maintain an inquiry into the bloodbath.
The Kingsmill atrocity got here amid a sequence of sectarian killings in Co Armagh.
Catholic brothers John Martin, Brian and Anthony Reavey have been shot useless of their house at Whitecross in south Armagh by the UVF on January 4 1976.
Three members of the Catholic O’Dowd household have been killed by gunmen on the identical night time because the Reavey household murders. Joseph O’Dowd, 61, and his nephews Barry O’Dowd, 24, and Declan O’Dowd, 19, have been killed, whereas Barney O’Dowd, father of the boys, was severely injured.
The Kingsmill assault occurred the next night time, on January 5 1976.
Mr Sherrard, in his findings added: “The assault, whereas ostensibly in direct response to the murderous assaults on the Reavey and O’Dowd households by loyalist terrorists on the night of January 4 1976, was not spontaneous however had been deliberate effectively prematurely.
“The IRA failed to interact with the Inquest. There was no acknowledgement by the IRA of the utter wrongness of the atrocity, its affect on these bereaved or the injury prompted to the complete neighborhood.
“Kingsmill was an overtly sectarian assault by the IRA. It was mounted as a result of the deceased males have been Protestants and for no different cause.”
The inquest ran for eight years.
Amongst these attending at present’s findings was Alan Black, who survived regardless of being shot 18 instances. He arrived in a wheelchair.
Karen Armstrong, the sister of sufferer John McConville, was additionally current.
Mr Sherrard dismissed any suggestion that perpetrators weren’t pursued as a way to defend an IRA informant, describing it as “unhelpful conspiracy theorising”.
“Such an assertion is totally with out basis,” he stated.
Two people recognized as suspects within the Kingsmill assault have been later given contentious so-called consolation letters issued by the UK Authorities to “On the Run” republican suspects throughout the peace course of.
Mr Sherrard insisted that the “OTR letters” had not impeded the inquest, as he highlighted that no agency proof connecting the people to the shootings had ever emerged.
The coroner outlined numerous errors and omissions within the police investigation within the wake of the capturing.
Nonetheless, he insisted these must be considered within the context of the time and stated there must be no try to shift the blame away from these accountable for the “brutal” murders.
“The investigation was not good,” Mr Sherrard stated.
“However its deficits may be put right down to the irregular safety setting of south Armagh in 1976, the extraordinary calls for on the police and the murderous competence of those that executed the atrocity and left with out a hint.”
He stated there may be “little doubt” that the seemingly suspects have been recognized to the safety forces on the time.
“However frequent data as to these with means and motive to hold out this heinous act doesn’t quantity to proof,” Mr Sherrard stated.
Mr Sherrard stated the Irish border was “exploited by terrorists” who carried out the Kingsmill assault.
He stated: “Every jurisdiction had its personal police, its personal navy and its personal legal guidelines.
“Regular policing was unattainable in South Armagh which, in distinction to the Republic of Eire, was in chaos as a consequence of terrorism.
“The Secretary of State for Northern Eire on the time of the assault, Merlyn Rees, citing the hostility of sure members of the native inhabitants, described the realm as ‘virtually uncontrollable’.
“The border allowed for planning, coaching, organisation, weapons storage and retreat at a protected bodily and authorized distance from the authorities that will be confronted with investigating terrorist acts in Northern Eire.”
Reacting to the findings, Doug Beattie stated the inquest “has failed at each stage”.
He stated it has “failed to offer the households confidence that they might obtain data into the lack of their family members, didn’t determine publicly these accountable for this horrific crime though they’re recognized.
“It additionally failed to maneuver the Irish authorities into lastly giving up their secrets and techniques into this vile episode of our troubled previous in an open and clear method.”
Mr Beattie added: “We now must look in direction of the UK Authorities and ask them to do the precise factor and maintain an inquiry into the Kingsmill bloodbath, making public the data that has been made recognized to them by way of the safety companies since that fateful day.
Former UUP MLA and Kingsmill campaigner, Danny Kennedy stated: “That is certainly a really darkish day for Alan Black and the Kingsmill households. They’ve each proper to really feel desperately indignant and let down, as I do, having supported their marketing campaign for justice over these lengthy years.
“The justice system has failed them.”
He added: “It’s nothing wanting disgraceful and disgusting that, after over 48 years of looking for solutions to what occurred at Kingsmills, we actually aren’t any additional on at present. I’m devastated.
“It’s now crucial that public representatives demand a full, unbiased public inquiry – nothing else will do.
“The blood of the harmless cries out from the bottom.”