The motorway murder of a prison officer in Northern Ireland is suspected to be the latest killing perpetrated by dissident republicans opposed to the peace process.
While the actions of the violent extremists remain sporadic, the ambush has provided a shocking reminder of both their lethal capacity and intent.
Since the Provisional IRA ceasefires of the 1990s, hard-liners have coalesced into various factions.
Only months after the signing of the Good Friday peace agreement in 1998 one of the radical groups - the Real IRA - killed 29 people, including a woman pregnant with twins, in a bomb in the Co Tyrone town of Omagh.
The structure and membership of the disparate gangs has remained fluid ever since, with crossover and co-operation common.
In July this year the Real IRA and Republican Action Against Drugs (RAAD) announced they had joined forces along with a number of unaffiliated individuals and would now be known as the "IRA".
Security chiefs believe that new group was responsible for two failed bombing bids in Londonderry in September.
Prior to this attack, there had been evidence of a decrease in dissident activity, with 20 national security attacks between January and October, compared to 25 in the same period in 2011.
While the threat level in Northern Ireland has remained at severe, last week the likelihood of a dissident attack in mainland UK was downgraded to moderate.
Before the shooting on the M1, the last security force member murdered was 25-year-old policeman Ronan Kerr in April 2011.