The Omagh bomb atrocity could and should have been prevented, the High Court heard yesterday.
Lawyers for the father of one victim claimed there was enough intelligence available ahead of the massacre.
Michael Gallagher is seeking to judicially review Northern Ireland Secretary Theresa Villiers’ decision to rule out a public inquiry into the attack.
His son Aiden was among 29 people, including a woman pregnant with twins, who died in the August 1998 outrage.
Together with relatives of some other victims, Mr Gallagher is campaigning for a cross-border probe into allegations that the security services could have done more.
They took their battle to court after Ms Villiers announced in September there were insufficient grounds to justify a further inquiry.
Mr Gallagher’s London-based senior counsel yesterday contended that the state is under a duty to investigate.
Central to the case are obligations contained within the Human Rights Act including duties of prevention and investigation under Article 2, which addresses right to life.
Ashley Underwood QC contended that much of the investigative material only emerged after the Act was brought in.
He set out a series of claims from intelligence sources that they told of terrorist plans in the run-up to the attack.
“There is an arguable case that the state could and should have prevented the atrocity at Omagh,” Mr Underwood said.
Reserving judgment on the application for a judicial review, Mr Justice Treacy said he would review submissions.