Gardai believe the group responsible for the Omagh bombing emerged last summer after the Provisional IRA called its second - and many believe permanent - ceasefire.
IRA" and "Oglaigh na hEireann". The telephone caller who gave the misleading information about the location of Saturday's bomb said he was from Oglaigh na hEireann.
The group has styled itself the "Real The group is believed to be led by a few figures said to be intensely opposed to the republican leadership of Mr Gerry Adams, Mr Martin McGuinness and Mr Pat Doherty which, effectively, delivered both ceasefires.
The group, gardai say, is the paramilitary wing of the breakaway political group, known as the 32-County Sovereignty Movement, which left Sinn Fein last year in protest at the party's support for the Belfast Agreement.
The group's chairman, Mr Francie Mackey, a councillor in Omagh, said last Friday there was no link between his group and the paramilitary group styling itself the "Real IRA".
As other minority paramilitary groups slowly move towards ceasefire positions, the "Real IRA" group has been emerging in recent months as the biggest threat to peace.
Its leaders, former senior Provisional IRA members, have access to the Provisional's arsenal of Semtex explosive and detonators, and have shown an increasing recklessness in the direction of their bombing campaign in the North.
Within two months of the Provisionals calling their second ceasefire the dissident group, then without any name or form of public image, detonated its first bomb near the RUC station in the mainly Protestant village of Markethill, Co Armagh.
The bombing target, just after another highly troubled summer in the North surrounding the Drumcree crisis, was highly provocative.
But on that occasion the RUC was able to clear the surrounding area and there were only a few minor injuries. The bomb was in a white Ford Transit van stolen in Dundalk.
Nothing further was heard from the group until January 5th when a 500lb bomb in a Ford Sierra, also stolen in the Republic, was defused at Banbridge, Co Down. Examination showed the bomb bore many characteristics of those used by the Provisional IRA since the early 1990s.
Provisional IRA technology was clearly being used but it was unclear if there was active Provisional IRA collusion in the attack.
Two days later the Garda Special Branch seized 1.5 tonnes of explosive in a disused factory at Howth.
Within three days in February car bombs exploded in Portadown, Co Armagh, and Moira, Co Down. The bombs caused extensive damage but few injuries, due to the efficiency of the RUC's clearance operations.
The bombs in Moira and Portadown were in a BMW car and four-wheel drive jeep - both stolen in the Republic. The dissidents were to steal and use the same types of vehicles for further attacks.
In March, gardai had the first of several successes against the group, capturing a 1,200lb bomb in a stolen Mitsubishi Pajero in Dundalk and a 600lb bomb in a Renault 21 in a shed in Hackballscross, Co Louth.
The bomb found in Dundalk was primed and ready to be driven North. Gardai believed the intention was to detonate it - possibly to cause civilian casualties - during the St Patrick's Day visit to the White House by the Sinn Fein president, Mr Adams.
The bomb was to be used to embarrass the Sinn Fein leader at a point when he was about to be welcomed back into the peace process by US President, Mr Bill Clinton.
Another 1,200lb bomb intercepted by the Special Branch at Dun Laoghaire ferry terminal as it was being taken to Britain - again in a stolen BMW - was intended to cause casualties at the Grand National just as the Sinn Fein leadership was about to sign up to the Belfast Agreement at Stormont.
But during the month the group launched two mortar attacks, in Armagh and Forkhill. These and subsequent mortar attacks revealed further the group's limited technical ability and the recklessness of its operations. In its last mortar attack, in the centre of Newry last month, a single 200lb mortar misfired and failed to explode.
The device was fired near the busiest part of the town's commercial centre. Had it gone off it could have caused many deaths and injuries.
The last two car bombings by the group, in Newtownhamilton, Co Armagh, on June 24th and on August 1st in Banbridge, Co Down, revealed what might now be seen as an increasing threat to civilians.
In both instances the warnings were less specific and more tightly timed than before. The RUC was barely able to clear the areas and in both cases there were dozens of minor injuries from flying debris.
Two other bombs were abandoned and made safe by the British army at the height of July's Drumcree loyalist stand-off.
Had either of these bombs gone off during the stand-off it could have precipitated a massive crisis.
Also during the summer the group began to use vehicles stolen inside Northern Ireland for its attacks and it appeared it had switched its bomb-making operations across the Border to escape Garda attention.
While the car used in Saturday's bombing was stolen in Co Monagahan the bomb might well have been prepared in Armagh before being transferred to Omagh.
So far, the year-old group has injured no members of the security forces in Northern Ireland but has committed the biggest single atrocity against the civilian population this century.
Opinion among security figures about the intention of the bombers on Saturday is divided.
It was pointed out that the earlier attacks had been at night but the last attack, in Banbridge, had taken place during the day. The Omagh bomb was also placed in the town's busiest shopping area at the height of one of the year's busiest shopping days.
Previous bombs had been aimed at mainly Protestant towns in the eastern part of Northern Ireland.
This tended to confirm the belief that the group was still confined to an operational base in the Border area between Dundalk and Newry.
Saturday's attack, if it was the work of the dissidents calling themselves the "Real IRA" or Oglaigh na hEireann, was the group's first attack in Tyrone.
It is believed the Garda's highly successful operations may have been insufficient to stop the group from spreading and that it might have established support and safe houses in Tyrone, possibly in Omagh.
The gardaI and RUC will try to assess how the group's ranks have swelled and how many disaffected ex-Provisional IRA members have been attracted to it.