Detectives investigating the murder of police officer Ronan Kerr believe they have identified the man who made the car bomb that killed him.
The dissident republican explosives manufacturer is based in the Republic of Ireland and is "experienced and competent" in constructing the deadly devices, according to a senior detective in the investigation.
The police team hunting the dissident republican gang behind the 2011 attack in Omagh also believe they know who directed the bomb team.
Officers have linked the murder of the 25-year-old freshly qualified constable to 16 other crimes committed by a number of inter-linked groups belonging to a dissident organisation that styles itself as the new IRA - among them two failed murder bids that seriously injured two other police officers and a car bomb attack on the Policing Board in Belfast.
Among those 16 offences, detectives have said they have gathered a significant amount of evidence linking three men to some of the most serious.
No charges have yet been brought against the men police today earmarked as key dissident suspects, in either Mr Kerr's murder or the other offences, explaining that more time is needed to build the cases against them. Fourteen arrests have been made in the investigation so far.
In an unusual step, the PSNI team outlined progress in the live investigation as the first man convicted as part of the wide-ranging probe, 36-year-old Gavin Coyle from Culmore Park, Omagh, was sentenced to ten years for offences linked to a dissident arms dump found in Coalisland, Co Tyrone days after Mr Kerr's death in April 2011.
Police claim the discovery of the arsenal, which the senior detective described as the biggest weapons find in a decade, saved lives, noting that hardware inside the lock-up garage, including taped-together loaded ammunition magazines, was in a state of readiness for use.
As well as giving details about the hunt for the killers of Mr Kerr, the PSNI released new information about the high explosive booby trap bomb that killed him.
They said magnets used in the bomb were sourced from a taxi sign stolen from a vehicle in the Arvalee area of Omagh two and a half weeks before the attack.
Detectives have insisted the sentencing of Coyle - for possession of explosives and firearms with intent to endanger life and membership of a proscribed organisation - only marks the end of one chapter of their investigation, characterising it as a "building block" on which to strive for further convictions.
Two and half years on from the Catholic policeman's death, officers believe the investigation could now run in excess of five years.
Its scale and complexity is massive. Officers have carried out 11,750 tasks or actions so far - that is already more than the 10,500 undertaken during the investigation into the Real IRA's 1998 Omagh bomb.
Almost 8,000 items have been seized for potential forensic examination - a process that is on-going - while reams of CCTV footage covering the area from Omagh to Coalisland around the time of the bomb have been reviewed. More than 1,500 doors have been knocked on in house-to-house inquiries.
The police are investigating a number of small dissident gangs, comprising around 20-25 individuals in total, based in the areas of Omagh; Coalisland; Toomebridge and Ballyronan on the northern shore of Lough Neagh; and Monaghan in the Irish Republic.
Officers believe all are inter-linked to certain degrees and that all take direction from leadership figures within the so-called new IRA in Belfast.
In a further layer of complexity, police think some of the dissidents use a criminal gang in Omagh to secure some of their hardware.
Among the 17 offences covered by the investigation are the attempted murders of Constable Ryan Crozier near Castlederg, Co Tyrone in May 2008 and Constable Peadar Heffron in Randalstown, Co Antrim in January 2010. Both officers sustained serious injuries, with Mr Heffron losing a leg.
Police believe the dissidents they are hunting were also behind the attack on the Policing Board in November 2009 when a car bomb partially exploded outside the Belfast headquarters of the PSNI's oversight body.
The arms dump over which Coyle was convicted was stored in a garage on the Mountjoy Road in Coalisland.
Items found inside included four AKM assault rifles (all were fully functional), semtex, timer power units used for detonating bombs, ammunition, incendiary devices, a booster pack for an RPG7 rocket, parts of an improvised PRIG grenade
Officers who raided the garage found that two ammunition magazines were loaded and taped together - a technique used to enable rapid fire and swift reloading.
Four vehicles were also found in the lock-up. Three cars had been stolen by masked men armed with handguns who held up a second hand dealership on the outskirts of Omagh in 2010.
A blue Ford Transit also stored in the garage had been hijacked from a newspaper delivery driver in Toome in the same year.
In two of the vehicles police found water bottles filled with petrol - indicative of preparations for setting them on fire after a crime.
In later searches by the investigation team in 2012, officers found the warhead of an RPG7 rocket (compliant with the booster found in the garage the year before) in a derelict building in Omagh. A handgun was found in a separate search.
Two arms hauls have also been discovered in Co Monaghan.