By Vincent Kearney
BBC NI home affairs correspondent
Dissident republicans murdered 29 people in Omagh in 1998
This Friday marks the 10th anniversary of the Omagh bombing, when the Real IRA detonated a car bomb that killed 29 people and injured hundreds of others.
It was the single biggest loss of life during the troubles.
Ten years on, the Real IRA and other dissident republican groups have vowed that their violence will go on. But just how great a threat do they pose?
"High on intent, but low on capability". That's been the consistent security assessment of the capabilities of republican dissidents for a number of years.
They have not killed a member of the security forces or carried out a significant attack of any kind since the Omagh bombing, but a number of events during the past year would suggest that their capabilities are growing, and so too their potential threat.
Dissident groups are believed to have about 80-100 active members.
A small hardcore are experienced terrorists who were previously members of the Provisional IRA, while the majority are committed to the dissident cause but lack operational experience.
It is estimated that there could be about 250-300 others willing to lend support and some assistance, while not wanting to become active terrorists.
There are small but relatively strong elements in Derry, Tyrone, Fermanagh and north Armagh.
They are believed to be attempting to recruit more experienced members, in particular former IRA bomb makers, but there is no evidence that they're being successful.
Dissidents haven't been able to form a central command structure and still operate as independent, fragmented factions carrying out attacks in their own areas.
It is also widely believed that the security services on both sides of the border have a number of well placed informants.
So what kind of threat do they pose, and could they commit another large-scale atrocity?
"We've been clear about the current threat for the last six months. The threat is high in certain parts of Northern Ireland," PSNI Chief Constable Sir Hugh Orde said.
"But they're badly disrupted, they're marginalised, they're fighting with each other so they are not at the same level and they don't have the capacity in our judgement to carry out an outrage on the scale of Omagh.
"But they still pose a threat to the public and to the police.
"Their focus is clear, they are determined to kill a police officer, they are focused on killing a police officer and that is where our efforts are going."
There is concern at the increasing variety of weapons and tactics being used.
In Lurgan last year, dissidents tried to attack police officers with a new kind of mortar that was more sophisticated than those previously used by the Provisional IRA.
There have been recent attempts to murder police officers
In November, they shot and wounded two police officers in Derry and Dungannon, and in May this year a police officer suffered serious leg injuries when a bomb exploded under his car near Castlederg.
It is understood that device contained a commercial explosive - not Semtex, which was used extensively by the IRA, a substance more powerful than homemade explosives.
In June, they packed more than 150 pounds of explosives into a milk churn and beer keg and planted them beside a small bridge near Roslea in county Fermanagh.
Two police officers lured to the area by a hoax phone call escaped death or serious injury because only the detonator exploded.
MI5 staff based in their new Northern Ireland headquarters in Holywood are responsible for countering the threat from dissident republicans.
To do that, the security services devote 15% of their resources to dealing with domestic terrorism.
It is widely believed that the security services on both sides of the border have a number of well-placed informants, and they have managed to disrupt a number of attempts to bring in large quantities of weapons from eastern Europe.
Dissidents are clearly determined to improve their capabilities and increase their activities, but Sir Hugh Orde believes the police are capable of dealing with that threat, and doesn't believe they are capable of sustaining a long-term campaign of violence.
Of course, many would have said the same thing about the Provisional IRA in its early days, but it became one of the deadliest terrorist groups in the world, killing more than 1,700 people.
However, the dissidents lack one key ingredient. They don't have anything like the kind of widespread support within the nationalist community that the IRA had during the Troubles.
History suggests that without that support, dissidents may well be able to periodically kill, shoot and bomb, but can't hope to make any real political impact.