Fears are growing that a new dissident threat may have been behind the murder of police constable Ronan Kerr.
Almost 72 hours after the brutal killing of the young police constable, no group has yet claimed responsibility for the atrocity.
Both Oglaigh na hEireann and the Real IRA have the type of bomb-making expertise described by the PSNI yesterday.
But so too does a group of disgruntled republicans recently believed to have defected from the mainstream IRA in Tyrone.
“We have real concerns about that area. There are serious concerns about leakage,” a source with knowledge of intelligence assessments told this newspaper.
However, the source could not confirm if those who have left the IRA have merged with one of the dissident groups.
A senior republican speaking to this newspaper suggested dissidents may simply be trying “to sew confusion”, but also pointed to the storm of condemnation that followed the weekend killing.
“It's interesting thus far that nobody has popped their head up to defend what happened or explain what happened,” the source said.
“I don't think they anticipated the backlash,” he continued.
“They probably hadn't thought about it. It may give them cause to think,” he said.
But the source believed a statement would emerge from those responsible: “I have no doubt it will.”
Meanwhile, it has emerged that Peter Robinson and Martin McGuinness are set to break new ground by attending the funeral |of PSNI Constable Ronan Kerr |together.
It will be the first time the province’s leaders will have combined to pay their respects to a murdered member of the security forces, who was a Catholic.
Stormont’s two most senior politicians believe the symbolism of their joint attendance will send a powerful message worldwide that they are united and determined to face down dissident |violence.
Last night a former senior Catholic police officer said talks with dissidents should not be ruled out.
Peter Sheridan, who held the rank of assistant chief constable, told the Belfast Telegraph: “Raw emotions at the moment will not allow it to happen now, but the possibility of dialogue should be kept open.
“If you look for a security response then the danger is you expect it to be 100%, which intelligence can't be.
“The response has to be wider thinking,” he continued.
“There have to be interventions with young people who are vulnerable to recruitment.
“And Catholic leaders need to ensure that support for policing is consistent and embedded within communities.”
“We need more than condemnation, important though that is,” Mr Sheridan, now chief executive of Co-operation Ireland, added.
Asked if he thought dissidents were deliberately targeting Catholic officers, Mr Sheridan replied: “It's hard to believe anything else.”
And he said those officers were “concerned and worried about their own safety”.
Yesterday police gave details of the bomb used in the weekend attack. Its components included high explosives and a tilt switch packed inside a plastic lunchbox.
It is a tactic used on scores of occasions by the IRA that has now been adopted by dissidents in their campaigns.
The Government vowed last night that the killers of the PSNI officer will not drag Northern Ireland back to the past.
During an emergency statement to the Commons, Northern Ireland Secretary Owen Paterson branded the Omagh car-bombing “a revolting and cowardly act perpetrated by individuals intent on defying the wishes of the people”.
But he pledged the PSNI would “not rest until these evil people are brought to justice”.
Shadow Northern Ireland secretary Shaun Woodward warned of a “new generation” of terrorists who were “bordering on psychotic” adding the “brutal assassination rekindles a deep wound” for the people of Omagh.