The car used to carry the Omagh bomb was stolen a week earlier in Carrickmacross, Co Monaghan, and gardai believe the dissident republican group styling itself the Real IRA or Oglaigh na hEireann was responsible.
Immediately after Saturday's attack, gar dai stepped up patrolling in the Border area and all available plain clothes officers in the Border divisions were brought on duty. However, there were no reports of arrests by last evening.
More structured policing responses to the threat from the dissident republicans are likely to emerge in the next few days follo wing today's meeting between the Garda Commissioner, Mr Pat Byrne, and the RUC Chief Constable, Mr Ronnie Flanagan.
Garda sources already anticipate the investigation into the largest single atrocity of the Troubles will involve the closest co-operation between the two forces in their histories.
Senior Garda sources agreed yesterday with their RUC counterparts that dissident republicans, based mainly in the Border area between north Louth and south Armagh, were responsible for the attack.
The group calling itself the Real IRA is the main target of attention. Gardai believe it has grown in size in recent months and may have spread into parts of Northern Ireland where it was not previously known to have a presence.
It is thought that while the car was stolen in Monaghan, the bomb could have been prepared north of the Border and the bombers could have been guided to their target by supporters in the Omagh area.
Yesterday, the RUC Chief Constable announced the setting up of a special task force to investigate the bombing, to be headed by Detective Chief Superintendent Eric Anderson. "He will be given additional uniformed and investigative resources that he can bring to bear in this investigation," Mr Flanagan said. "No stone will be left unturned until we bring these people to justice."
He said the investigation would concentrate on the Real IRA. "It's fair to say our focus at this point in time would be on those that call themselves the 32-County Sovereignty Movement and those close to them.
"They are out to murder people for the sake of murdering people. That's exactly what they did yesterday," he told the BBC's Breakfast with Frost yesterday.
Supt Anderson, who is acting Assistant Chief Constable in charge of crime, led the investigation into the killing of seven customers in a pub in Greysteel, Co Derry, in 1993. Three loyalists were arrested shortly after and sentenced to life imprisonment.
"I, like so many other people, thought this was over," he said. "I never thought I would be back to heading this sort of investigation, but I can assure people that everything will be done; all resources will be poured into this investigation. I am of the opinion every contact leaves a trace."
He confirmed that detectives were following the theory that dissident republicans were behind the bomb and the investigation would begin with a painstaking examination of the scene.