A judge has recommended the British government carry out an investigation into the Omagh bombing, and urged the Dublin government to do likewise, after finding "plausible arguments" that there was a "real prospect" of preventing the atrocity.
Delivering judgment in a legal challenge against the British government's refusal to hold a public inquiry, Justice Horner said a human rights compliant probe was needed to examine whether a more "proactive" security approach against dissident republican terrorists in the lead-up to the Real IRA bombing may have thwarted it.
The outrage in August 1998 killed 29 people, including a woman pregnant with twins. It was the worst single atrocity of the Troubles.
Eight years ago, Michael Gallagher, whose son Aiden was killed in the blast, launched the judicial review against the British government's refusal to order a public inquiry into security failings prior to the bombing.
Delivering the long-awaiting judgment in Belfast High Court, Mr Justice Horner said: "I am satisfied that certain grounds when considered separately or together give rise to plausible allegations that there was a real prospect of preventing the Omagh bombing.
"These grounds involve, inter alia, the consideration of terrorist activity on both sides of the border by prominent dissident terrorist republicans leading up to the Omagh bomb.
"I am therefore satisfied that the threshold under Article 2 ECHR (European Convention on Human Rights) to require the investigation of those allegations has been reached."
Judge Horner said he was not going to order that the probe take the form of a public inquiry, explaining that he did not want to be "prescriptive".
He also said he did not have the powers to order the authorities in the Republic to act, but he expressed hope the Dublin government would take a decision to investigate events around the bombing.
"I am not going to order a public inquiry to look at the arguable grounds of preventability," he said.
"I do not intend to be prescriptive. However, it is for the government or governments to hold an investigation that is Article 2 compliant and which can receive both open and closed materials on the designated grounds."
The judge added: "It is not within my power to order any type of investigation to take place in the Republic of Ireland but there is a real advantage in an Article 2 compliant investigation proceeding in the Republic of Ireland simultaneously with one in Northern Ireland.
"Any investigation will have to look specifically at the issue of whether a more proactive campaign of disruption, especially if co-ordinated north and south of the border, had a real prospect of preventing the Omagh bombing, and whether, without the benefit of hindsight, the potential advantages of taking a much more aggressive approach towards the suspected terrorists outweighed the potential disadvantages inherent in such an approach."
In a brief hearing, Mr Justice Horner only read the conclusion of his judgment to Belfast High Court today.
He explained he was unable to read the full open judgment setting out his reasoning because the person whose job it was to check the document to ensure it did not contain sensitive material was self-isolating with Covid-19.
Mr Gallagher launched his action against former secretary of state Theresa Villiers after she declined to order a public inquiry.
Ms Villiers argued a probe by former police ombudsman Dr Michael Maguire was the best way to address any outstanding issues.
In the legal case, Mr Gallagher claimed that intelligence from British security agents and RUC officers could have been drawn together to prevent the dissident republican bombing.
On August 4 1998, 11 days before the bombing, the RUC received an anonymous telephone call warning there would be an "unspecified" terrorist attack on police in Omagh on August 15.
The force's Special Branch, which handled intelligence from agents, took limited action on the information and a threat warning was not sent to the sub-divisional commander in Omagh, an investigation by former police ombudsman Baroness Nuala O'Loan found.
An RUC review concluded in 2000 that the information should have been passed to the commander.
Stanley McCombe, whose wife, Ann, was killed in the Omagh bombing, said the ruling gives the families "some hope".
"It took some time for it to sink in," Mr McCombe said.
"We are delighted that the judge has come out and said that there is a possibility of an investigation into the prevention of the bomb.
"It's fantastic news but we have known this and survived this for the last 20 years.
"The amount of work that myself, Michael and our legal teams in getting to the court and it is only rightly so that we get an investigation in this.
"This is a step forward. But why has it taken this length of time for us to get the public inquiry?
"What are the British and Irish governments hiding? Why do they not want an inquiry when it is the worst atrocity in Ireland?
"The worst part about it was it was in peacetime, not in Trouble times."
Responding to the judgment, Secretary of State Brandon Lewis said: "The Omagh bombing was a terrible atrocity that caused untold damage to the families of the 29 people who were tragically killed and the 220 who were injured. The reverberations of that awful event were felt not just in Northern Ireland, but across the world.
"I want to put on record my deep regret that the families of those killed and wounded have had to wait so long to find out what happened on that terrible day in 1998. They deserve answers and I have great respect for their patience, grace and determination.
"We recognise that today the court has set out that there are 'plausible allegations that there was a real prospect of preventing the Omagh bombing' and that more should be done to investigate this.
"The UK government will take time to consider the judge's statement and all its recommendations carefully as we wait for the full judgment to be published."
Taoiseach Micheál Martin said the Dublin government would do what is "necessary" following the ruling.
"We will analyse that judgement and we will do what is necessary in terms of the citizens on the island of Ireland," he told reporters.
"I always stand ready to have an open book in terms of any atrocity that was committed which had a cross-border dimension to it in terms of following through in any way we can through the provision of information or indeed to vindicating the rights of people and citizens.
"So, a very open book in terms of how we proceed with this now but we've got to examine the options that are available to us in respect of the conclusions."
The taoiseach said the judgment demanded "very serious reflection and analysis" by both the British and Dublin governments.
"That was the single worst atrocity that occurred - it was appalling and the responsibility is on those who committed that foul act," he said.
"So many, many people lost their lives. That said, there's an obligation on governments to examine what could have been done, if anything could have been done to prevent the atrocity with a view to informing future practice.
"But I'm in no doubt that evil people did that, it was just absolutely reckless and appalling and gave such heartache and broke so many families - a needless loss of life when we were on well on our way to a peace process and we should never lose sight of those who are ultimately responsible in the first instance.
"It's those who perpetrated the crime itself, who thought up the idea, who planted the bomb and left such devastation behind them, we can never lose sight of that, they're fundamentally guilty in terms of murdering so many people.
"But the state must always self-reflect in terms of how it acts to protect its citizens."
Mr Martin highlighted that the Dublin government had previously fulfilled its obligations in respect of investigating crimes with a cross-border dimension when it set up the Smithwick Tribunal to probe allegations of Garda collusion in the IRA killings of two senior RUC officers during the Troubles.
"We will do so again in respect of any further investigations that we support and cooperate with," he said.
"But I think we have to take one step at a time, we have to analyse what the implications of this are, reflect on the judge's conclusions and how we can take it forward from here."
