The British Government is to seek to have some intelligence gathered on the Omagh bombing assessed in private, the High Court heard today.
Northern Ireland Secretary Theresa Villiers plans to apply to have a closed material procedure form part of a challenge to her refusal to hold a public inquiry into the atrocity, a judge was told.
Confirmation of the move came as lawyers for the father of a young man killed in the Real IRA attack accused the authorities of "massively dragging their heels".
Michael Gallagher has mounted a legal action in a bid to force the government to order a full inquiry.
His son Aiden was among 29 people, including a woman pregnant with twins, killed in the August 1998 outrage.
In September 2013 Ms Villiers rejected calls for a public investigation, deciding instead that a probe 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, Co Monaghan, is currently charged with the 29 murders which he denies.
Central to the bid to have Ms Villiers' decision judicially reviewed is a contention that the British Government has a duty under Article 2 of the European Convention on Human Rights to protect lives and investigate the bombing.
Mr Gallagher's lawyers claim a range of intelligence from British security agents, MI5 and RUC officers could have been drawn together to stop the killers in their tracks.
An alleged gap in the information relates to any monitoring of the bomb and scout cars as they crossed the Irish border into Omagh on the day of the attack.
It has been suggested that a BBC Panorama documentary has raised the possibility of other intelligence than the intercept material which has been the subject of investigations to date.
In court today Paul Mclaughlin, for the Secretary of State, confirmed her intention to seek a closed material procedure before the full hearing can take place.
The process, brought in under the Justice and Security Act, can assess whether public disclosure of some information would be damaging to national security.
But with the other side in proceedings kept in the dark about the contents, some have claimed it could give rise to secret courts.
Mr McLaughlin stressed that a special advocate has to be appointed by the Advocate General for Northern Ireland before the application is made.
He added that an "intensive" review of all available material has been carried out.
"We have been going through a difficult process of trying to work out what evidence there is, and what evidence can be served in open as opposed to what is required to be filed in a closed hearing," the barrister said.
"We are trying to put together an enormous jigsaw of what material exists and who it has been examined by."
During exchanges Mr Justice Treacy emphasised how the case centred on whether all intelligence material was made available.
"If the intelligence services don't know what they shared and who with, that would be deeply troubling," he said.
Ashley Underwood QC, representing Mr Gallagher, argued that the Secretary of State should have already notified the Advocate General.
Instead, he claimed: "She has just been sitting on her hands."
Mr Underwood also contended delays in the process were "ludicrous".
Attributing no blame on the government's legal representatives, the barrister added: "I have no doubt there are people behind them that are dragging their heels, but nonetheless heels are being dragged massively."
The case was adjourned for a further review in two weeks time.