A public inquiry into the infamous Omagh bombing would uncover "unnerving secrets" of security force failings, said one of those bereaved by the atrocity.
Michael Gallagher and other Omagh victims presented Northern Ireland Secretary of State Owen Paterson with a specially commissioned report claiming the atrocity could have been prevented.
The families campaigning for a cross-border inquiry will now seek meetings with the Chief Constable Matt Baggott and Justice Minister David Ford to brief them on the consultants' report into the case.
Gallagher, whose son Aiden was killed in the bombing, said both the Irish and British governments would continue to face calls for a public inquiry and any refusal to respond positively to the new evidence would be brought to the courts.
Twenty-nine people, including a woman pregnant with twins, were murdered in the Real IRA atrocity in 1998. No-one has been successfully criminally convicted of the attack in the County Tyrone town.
"I think that the government are going to have some difficulty with granting a public inquiry into Omagh because it will unearth some very unnerving secrets”, said Gallagher.
"But we feel, and we told the Secretary of State, that there will be uncomfortable truths for both the British and Irish governments. But that is nothing to what the families have had to suffer”, he added.
His comments came after a meeting with the Secretary of State at Hillsborough Castle.
The families said their report brought together all available evidence on the case and showed authorities on both sides of the border could have prevented the car bombing.