Detectives hunting the Omagh bombers are to put republicans support for Northern Ireland's police service to the test with a series of newspaper adverts urging full co-operation.
With investigators seeking information on the Vauxhall Cavalier used by Real IRA terrorists to kill 29 people in August 1998, the new appeal is directed at those living on either side of the Irish border where the car travelled through.
Only one man, south Armagh electrician Sean Hoey, 37, has been charged with the Omagh atrocity. He is waiting a judge`s verdict after standing trial in Belfast for the murders.
But after Sinn Fein`s historic declaration in January that it will embrace policing arrangements in Northern Ireland, the detective in charge of the bomb inquiry is attempting to break down a wall of silence which has shielded other dissident republicans involved.
Chief Superintendent Norman Baxter has decided to place a series of adverts in daily and weekly newspapers in Northern Ireland and the IRepublic this week, asking people in border areas to think again about coming forward with information.
The move has been fuelled by the changed outlook towards policing among a substantial part of the republican community, and the inquiry team`s determination to seek justice for the bomb victims, Mr Baxter confirmed.
He said: "It`s eight and a half years since the Omagh bombing but the investigation is continuing.
"In the light of recent changes in attitude from certain groups towards policing, I think it is important to ask everyone to think again about coming forward with information about what happened.
"I would encourage public representatives to use their influence in the communities which they represent, on both sides of the border, to ask people to come forward."
He added: "We are particularly interested in the movements of the bomb car in the days leading up to the atrocity.
"We want to know about the movements of the red/maroon Vauxhall Cavalier between Thursday 13 August 1998 and Saturday 15 August 1998, the day of the explosion which killed 29 innocent people.
"Anyone who knows anything about the movements of this car in the Carrickmacross area or the Louth/south Armagh area during this period is asked to contact the Incident Room at Omagh police station, telephone 028 8225 6682 (048 8225 6682 from the Republic).
"Any information will be treated in confidence."