A High Court judge has reversed the decision to throw out a damages claim brought by the husband of one of the Omagh bomb victims.
Laurence Rush's wife Elizabeth was among 29 people killed in the atrocity.
The ruling allows him to proceed with his action for damages against the police and government.
He sued the NI Chief Constable and Secretary of State for failures in the apprehension, detection and arrest of the Real IRA men responsible.
He also claimed for loss and damages, alleging that police failed to act upon information received on the August 1998 bomb plot, and did not give adequate warnings or implement sufficient evacuation procedures.
His case appeared to have failed last May when a High Court master granted an application by the defendants to strike it out on the basis that it disclosed no reasonable cause of action, or that it was "frivolous or vexatious".
It was held that the claim was unsustainable and without the potential for success.
However, Mr Rush's lawyers appealed that decision, instructing high-profile barrister Michael Mansfield to lead their challenge.
In the event the judge did not require to hear from Mr Mansfield before deciding that the case should go to trial.
Mr Justice Gillen is expected to give written reasons for his decision in due course.
The case centres on the duty of care owed by the police, in the course of carrying out its functions of investigating, controlling and preventing the incidence of crime.
The core principle established in leading cases is that, in general, officers should be immune from litigation for activities in investigating suspected crimes.
Counsel for the defendants pointed out that Mr Rush's lawyers were seeking to make it an exception because of the alleged information available to police and the scale of the bomb.
David Ringland said: "The fact that more than one person did die or could have died and that (allegedly) wouldn't have happened if there had been some form of intervention beforehand had nothing to do with the law as to whether there is an exception or not to the core principle."
However, Mr Justice Gillen upheld the appeal, prompting Mr Mansfield's only submission when he said to the judge: "Thank you."
Mr Rush did not attend the hearing due to ill health.
Outside the court, his solicitor Des Doherty said the case "potentially had ramifications for quite a number of cases in the north of Ireland involving the security forces."