The father of a young man killed in the Omagh bombing has won the legal right to challenge the government's refusal to hold a public inquiry into the atrocity.
No-one has been found guilty of the Real IRA bomb attack in August 1998, in which 29 people were killed.
A High Court judge ruled that Michael Gallagher has established an arguable case that the authorities are in breach of an investigative obligation.
A full hearing will be held in April.
It will explore claims that intelligence may exist to back Mr Gallagher's belief that the attack could have been prevented.
Mr Gallagher's son Aidan was one of the victims of the atrocity.
In September 2013, Northern Ireland Secretary Theresa Villiers rejected calls for a public inquiry, saying an investigation by Police Ombudsman Michael Maguire was the best way to address any outstanding issues.
Last October, Dr Maguire published a report where he found RUC Special Branch withheld some intelligence information from detectives hunting the bombers.
No-one has ever been convicted of carrying out the attack, but Seamus Daly, a 44-year-old bricklayer from Cullaville, County Monaghan, is currently charged with the 29 murders which he denies.
Central to the bid to have Ms Villiers' decision judicially reviewed was a contention that the government has a duty under Article 2 of the European Convention on Human Rights to protect lives and investigate the bombing.
Mr Gallagher was in court with his family and Stanley McComb, who lost his wife Ann in the blast, to hear his lawyers claim that the terrorist attack was at least arguably preventable.
They argued that a range of intelligence from British security agents, MI5 and RUC officers could have been drawn together to stop the killers.
Counsel for the secretary of state said that four separate Police Ombudsman examinations into Omagh had already been held.
In the latest report Dr Maguire concluded nothing had been identified which could have prevented the atrocity, but that Special Branch had acted "cautiously".
Further opposition to the challenge was based on the date of the bombing - two years before human rights legislation was incorporated into UK law in 2000.
But granting leave to seek a judicial review, Mr Justice Treacy held that Article 2 duties were at least arguably engaged.
He also decided an arguable case had been established that the state was in breach of its obligation to conduct such an investigation into claims the attack could have been prevented.
The judge listed the case for a substantive two-day hearing on April 29-30.
Outside court, Mr Gallagher expressed delight at the outcome.
He said: "This is but a step on our continued fight for justice. Today the courts have agreed at the very least that the secretary of state's decision was questionable.
"We will now move on to prepare for a full hearing to show the state has yet to properly investigate the circumstances of the Omagh bomb."
The decision was also welcomed by Amnesty International.
"What the families, and Northern Ireland more broadly, deserve is the fullest account possible of what happened in Omagh," Amnesty's Patrick Corrigan said.