The murder of County Armagh man Paul Quinn was a barbaric deed which was evil and inexcusable, the Catholic Primate of All Ireland has said.
Dr Brady said there was a duty before God to pass on information
Archbishop Sean Brady said there should be no reprisal for the killing.
Mr Quinn, 21, died after being beaten by nine men with iron bars at a farm shed in County Monaghan on Saturday. His funeral will be held on Thursday.
Martin McGuinness has spoken to Prime Minister Gordon Brown and Irish Foreign Minister Dermot Ahern about the murder.
The deputy first minister said he had assured them republicans were not involved in the murder and again called for anyone with information to give it to the police.
"The people who murdered Paul Quinn are criminals, they need to be arrested and there is a duty and a responsibility with everyone with any scintilla of information whatsoever to bring that information forward to both the Garda and the police here in the north," he said.
Mr Quinn's family blamed the killing on the IRA.
A post-mortem examination carried out on Tuesday confirmed the injuries which caused his death were consistent with a serious assault.
Archbishop Brady said the murder had "shocked and appalled a whole community".
'Tyranny of violence'
Offering his sympathy to Mr Quinn's grieving family, he said the death "caused revulsion and shame in all right-minded people".
Mr Quinn was found at farm buildings near the village of Oram
"It shows a total lack of respect for the God-given gift of human life," said the Archbishop.
"I hope that those who carried out this atrocious crime will soon be apprehended and brought to justice.
"Those with information have a duty before God to pass it on to the Gardai or PSNI. The tyranny of violence and intimidation must be defeated."