Constable Kerr died when an under-car bomb exploded outside his home in Omagh, Co Tyrone, as he prepared to drive in work in April 2011.Despite numerous arrests in the case, no charges have yet been brought.But, as UTV's Mark McFadden reports, police do believe that major steps forward have been taken in their investigation."They've discovered a network of dissident republicans in and around Omagh - in Coalisland, in Toomebridge, even across the border in Monaghan," Mark McFadden said."They're all reporting back to a central dissident command in Belfast."Regarding the man who actually made the device used in the murder of Constable Kerr, it is understood that detectives believe they know his identity and that he is living in the Republic.Police are determined to get it right.Mark McFadden, UTVCriminal gangs are said to be 'helping' dissident republicans, by stealing cars to be used in gun and bomb attacks and by providing weapons or even money.For example, the magnets used to attach the bomb to the underside of Constable Kerr's car were taken from a stolen taxi sign.Police believe that they are slowly, but painstakingly building a detailed picture of the operation responsible for the murder of one of their colleagues."Detectives are going to move carefully and deliberately," Mark said."They're determined to get it right."The details regarding the case come as an Omagh man was jailed for 10 years over a haul of weapons, explosives and ammunition discovered by the detectives investigating the murder.Gavin Coyle, 36 and from the Culmore Park in the Co Tyrone town, admitted membership of an organisation calling itself the 'New IRA'.He was linked to the arms find by DNA evidence and by explosives residue on his clothes.