The killers of Mr Matthew Burns, who was shot dead last Thursday, have been condemned as inhuman and unjust "dealers in death".
Mr Burns (26) died when gunmen attacked him and his brother, Patrick, as they sat in a car near their home outside Castlewellan, Co Down.
Mr Patrick Burns suffered gunshot wounds and was treated in the Downe hospital in Downpatrick. Father Albert McNally, parish priest of the neighbouring parish of Maghera, Co Down, of which Mr Burns was a member, said the local community denounced the murder.
He was speaking at the requiem Mass yesterday at St Malachy's church, Castlewellan, and described the killing as a summary execution.
The dead man had survived a bomb attack and a paramilitary punishment attempt within the past two years. A second brother of Mr Burns, Seán, was to have been in the car with them but he had stayed at home just 200 yards from the murder scene as he had flu.
Mr Burns was a keen kickboxer and a pair of gloves adorned his coffin during the Mass before it was taken to Aughlisnafin cemetery a few miles away for burial.
Sinn Féin has insisted that the Provisional IRA did not shoot dead Mr Burns, but the PSNI Chief Constable has not ruled out involvement by that organisation.
The police have said the killing was meticulously planned but that it was still too soon to say who carried it out.
The Northern Secretary has also refused to speculate. Opening a new police station in Moira, Co Down on Saturday, Dr John Reid said he was awaiting a full security assessment from police.
"It is too early to make a firm commitment," he said. Referring to rumour that the murder was drugs-related, he added: "I am aware of the speculation about the Castlewellan murder.
"There are only implications for the ceasefire if we can discover who is actually behind this.
"Obviously we keep the ceasefire under review constantly for all of the groups." The murder has been condemned by the North's security minister, Ms Jane Kennedy.