The PSNI says its focus is on the New IRA after a senior officer was shot while off-duty in Omagh.
Detective Chief Inspector John Caldwell was shot multiple times outside a sports centre as he loaded footballs into the boot of his car.
Police said the focus of the investigation is on dissident republicans and “within that a primary focus is on the New IRA”.
Three men aged 38, 45, 47 have been arrested in connection with the attempted murder.
What is the New IRA?
There have been many “IRAs” over the previous 100 years, mainly formed through various factions and divisions of groupings.
The New IRA is believed to be the largest of the dissident republican groupings. It has been linked to a number of murders including those of journalist and author Lyra McKee in 2019, PC Ronan Kerr in 2011, and prison officers David Black in 2012 and Adrian Ismay in 2016.
The group is believed to have been formed between 2011 and 2012 following the merger of a number of smaller groups, including the Real IRA - the group behind the 1998 Omagh bomb.
The group is strongest in Londonderry and Strabane, with a presence in Belfast, and other pockets in Co Tyrone, and Lurgan in Co Armagh.
What is the recent history of the New IRA?
In August 2020, the alleged leadership of the New IRA suffered a major blow with a series of arrests prompted by an MI5 surveillance operation.
Less than a year before, in September 2019, a bomb in an "advanced state of readiness" was found in the Creggan area of Derry.
Police said the device, attributed to the New IRA, was designed to kill police officers.
In June 2019, the group claimed responsibility for the failed murder bid of a police officer after an unexploded bomb was found under the officer's car parked at Shandon Park Golf Club in Belfast.
In April that year, the New IRA claimed responsibility for shooting dead Ms McKee who was observing rioting in the Creggan area.
A few months after the murder of Ms McKee, Assistant Chief Constable Barbara Gray, the officer in charge of the Police Service of Northern Ireland's anti-terror response, said the New IRA derived "sick and sad" pleasure in the reaction to the shooting, motivating them to intensify their activities in the region.
Ms Gray expressed regret that the public outcry following the murder of the 29-year-old did not act as a watershed moment for the dissidents to reconsider their adherence to violence.
She claimed the reverse has been true, saying the killing in Derry's Creggan area was a factor in a spike in dissident murder bids in the region.
A month before the murder of Ms McKee, the New IRA claimed responsibility for sending small explosive devices in the post to two airports and a train station in London and to the University of Glasgow.
In January 2019, police blamed the New IRA after a bomb placed in a van exploded outside the courthouse in Derry.
Meanwhile, in 2020 a senior republican said New IRA threats against Sinn Fein were "stupid" and "dangerous".
At the time, all party members were warned of a dissident plot to launch an under-car bomb attack.
Gerry Kelly said it would not deter elected representatives but would worry members of their families.
Michelle O'Neill, then Stormont's deputy First Minister, said officers had warned that dissident republicans were planning to attack her and Mr Kelly.
It came in response to the pair's attendance at a Police Service of Northern Ireland recruitment event.
Dissident republican terrorist activity has been at a lower level in Northern Ireland in recent years and security services have secured a number of successes disrupting the activities of terror groups.
Last March, the level of terrorism threat from dissident republicans was lowered from severe to substantial for the first time in 12 years.
The decision to change the threat level was announced by the then-Secretary of State Brandon Lewis but made independently by the security service MI5.
The level is subject to continuous review and judgments are based on a wide range of information.
This was the first time the threat level in Northern Ireland was reduced from severe since it was first published in 2010.
Substantial means a terror attack is likely and could occur without warning.
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