Omagh car bomb leaves Northern Ireland on high alert
Northern Ireland security forces have for months been on a high state of alert against such dissident attacks, with three separate small groups active on an almost weekly basis.
But the murder of Ronan Kerr, a 25-year-old probationer, in the Co Tyrone town on Saturday afternoon, is the first fatality they have inflicted for some time, although they have killed some of their own members and caused widespread disruption with abortive bomb attacks and hoaxes.
The groups, known as the Real IRA, Continuity IRA and ONH, have caused growing concern to the security forces as they have grown in size, and in their capacity to produce car bombs and boobytraps of the type which killed the police officer.
His death will be seen as a setback for the policy of producing a more representative police serving through the recruitment of more Catholic officers.
Sinn Fein leader Gerry Adams said that the killing should not deter nationalists from continuing to join the police, and appealed for anyone with information to come forward.
The fact that the attack took place in Omagh has a particular resonance in that it was the location of the bomb which killed 29 people and two unborn babies in 1998. That too was the work of dissidents.
Constable Kerr was among an influx of several thousand officers who joined in a successful recruiting drive which over a decade has seen the number of Catholics in the ranks rise to 30 per cent.
The attack confirms that the dissidents pose a lethal threat, even though the Police Service of Northern Ireland, together with police in the Irish Republic, have had various successes against them over the past year.
A number of seizures of terrorist material have been made, with numerous arrests and a variety of charges brought. It is also assumed that the police and MI5 are making determined efforts to undermine the groups by infiltrating agents into their ranks.
But the enhanced threat meant that in February the authorities had to allocate almost a quarter of a billion pounds, over a four-year period, for additional security. Police said the money would be spent on investigation, more detectives, more equipment and air support.
This followed last September's admission by the head of MI5, Jonathan Evans, that the intelligence community had wrongly assumed "that the residual threat from terrorism in Northern Ireland was low and likely to decline further".
Instead, he said, there had been a persistent rise in the activities and ambitions of terrorist groups, with improved weapons capability and growing cooperation between them.
The groups have shown themselves capable of surviving even though their members are thought to be only in the hundreds. They have no real political support, and are not even contesting the elections to the Northern Ireland Assembly which are to be held in a month's time.
Those condemning the weekend attack encompassed major political figures on both sides of the Irish border and both sides of the Atlantic. David Cameron, US Secretary of State Hillary Clinton and Irish Prime Minister Enda Kenny joined the condemnation, as did major church figures.
The Democratic Unionist party and Sinn Fein, which together head the Belfast administration, were strikingly united in their condemnation, taking evident care not to allow the killing to divide them.
The DUP leader Peter Robinson said: "This was a young man who was bravely entering the police service, recognising that he was putting his life on the line. The overwhelming number want to move on – it's only a few Neanderthals who want to go back. They will not drag us back to the past."
Some of the most striking language came from Adams, whose Sinn Fein party was once completely opposed to the police but now formally supports it.
Adams said he had heard strident condemnations from lifelong republicans who believed the continuing violence was futile, adding: "The people who I know, and who I have known all my life, are seething with anger. They just feel outright anger. So there should be no room, or any tolerance, equivocation, justification for what has occurred."
Chief Constable Matt Baggott said: "I know my abhorrence and anger at such a waste of a good life is shared across the world."
Constable Kerr entered police training college in May 2010, and began his on the job training in December last. Prayers were said for him at vigil masses throughout Omagh on Saturday night.
Dissident Republican attacks
* March 2009: Two British soldiers shot dead outside Massereene Barracks in Co Antrim.
* April 2009: The Real IRA shoots a convicted rapist in the legs in Derry.
* September 2009: The PSNI finds a 600lb bomb left near the border village of Forkhill in Co Armagh.
* February 2010: Kieran Doherty murdered by the Real IRA.
* August 2010: Three children injured after a bomb explodes in a bin in North Street, Lurgan, Co Armagh.
* October 2010: Two men are shot in the legs in two attacks in Derry in the space of 48 hours.
* December 2010: Policeman finds an unexploded grenade outside his home in Co Fermanagh.
* April 2011: Ronan Kerr killed after a bomb explodes under his car outside his home in Omagh, Co Tyrone.