Former or current Provisional IRA members were involved in the murder of south Armagh man Paul Quinn last month, the Independent Monitoring Commission (IMC) said today.
John Grieve of the IMC
However, the IMC said it was too early to say if the killing had been authorised by the IRA leadership.
Sinn Féin has insisted there was no sanction for the murder from IRA leaders.
Minister for Justice Brian Lenihan said last month he had information that the killing had not been sanctioned or authorised by any paramilitary organisation.
Mr Quinn (21) from Cullyhanna, Co Armagh, was beaten to death with iron bars by up to nine men on a Co Monaghan farm last month after being lured there.
John Grieve of the IMC said today he believed the killers had IRA connections.
"Despite the fact that we are saying it is a local dispute, we do believe that those who were involved in the attack on him - in his brutal murder - included people who are members or former members or have associations with members or former members of the Provisional IRA," said Mr Grieve.
No one has yet been charged with the murder, but the PSNI Deputy Chief Constable, Paul Leighton, said recently that most of the suspects come from the North.
Mr Grieve said the IMC had yet to determine whether or not the murder was sanctioned by the IRA's leadership.
Sinn Féin MP Conor Murphy dismissed Mr Grieve's accusation.
"It is evidence not speculation that is needed to convict the killers of Paul Quinn. Sinn Féin have already said that anyone with information about the murder should bring it forward to allow due process and justice for the Quinn family."
An Ulster Unionist peer tonight used the protection of Parliamentary privilege to name a number of men who he claims were behind the murder.
Lord Laird's claims came during a House of Lords debate. He said the murder resulted from a dispute between Mr Quinn and a son of "a local IRA chief".
Additional reporting: PA