The Archbishop of Armagh and Cardinal designate, Seán Brady, has described the weekend murder of Paul Quinn as a barbaric deed that was evil and inexcusable.
Archbishop Brady also said those with information 'have a duty before God' to pass it on to gardaí or the PSNI.
The Catholic Archbishop made his appeal as a complex cross-border investigation into the death of the 21-year-old Armagh man continues.
A gang of seven or eight men beat Mr Quinn after luring him to a farm at Tullycora near the village of Oram on Saturday evening.
He was conscious when he was found by gardaí, but died two hours later in hospital.
Both gardaí and the PSNI are investigating what led to Mr Quinn's death, and although gardaí have the lead role in the investigation as Mr Quinn died in the Republic, it is believed his attackers came from Co Armagh.
Investigators are seeking the co-operation of a number of the 21-year-old's acquaintances who were used to lure him to a Co Monaghan farmyard.
Any links to an incident two weeks ago when a truckload of diesel overturned on a Co Down road and the driver set the fuel alight before absconding will also be examined.
Earlier, Northern Ireland First Minister Ian Paisley called for British Prime Minister Gordon Brown's full support if it turns out the IRA was involved in the murder of the Co Armagh man.
Mr Quinn's parents claim the organisation was involved in the death of their son.
The DUP insists proof ogf IRA involvement could collapse the political institutions. However Sinn Féin President Gerry Adams has denied any republican role in the killing.
