Thomas "Slab" Murphy approved the brutal killing of Paul Quinn in County Monaghan, an Ulster Unionist peer told the House of Lords under parliamentary privilege last night.
Lord Laird claimed that Armagh man Mr Quinn, 21, had been involved in a dispute with a man the peer described as "the son of a local IRA chief", and that a coterie of republicans - including Murphy - gave the go-ahead for the young man's "execution".
Moreover, Lord Laird told the House of Lords that Murphy subsequently ordered republicans in south Armagh not to speak to the police or PSNI.
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Claims: Thomas 'Slab' Murphy (right) under pressure over claims he approved the brutal execution of Paul Quinn
Mr Quinn, 21, was lured from his home at Cullyhanna, Co. Armagh, to a farm near Castleblayney on October 20, and was beaten with bars by a gang of up to 15 thugs.
There has been concern that power-sharing at Stormont between Sinn Fèin and the DUP could be jeopardised if family claims that the mainstream IRA was behind the killing are proved.
The UUP peer alleged the killing resulted from a dispute between Mr Quinn and a son of Vincent Traynor, "a local IRA chief".
The peer claimed: "Vincent oversold the case against Paul. Several weeks ago, Traynor asked the republican leadership, which included Peter and Patrick Quinn who ran most of the illegal fuel laundering plants in south Armagh for the IRA, to have Quinn executed."
Lord Laird went on: "After consulting with PJ Caraher and his son Michael, Thomas "Slab" Murphy, the Provisionals' commander in the area, Se·n Gerard Hughes, known as "The Surgeon", and James McArdle, permission for the execution was given."
He told peers: "Almost 20 republicans were present at the murder, as executioners, look-outs, drivers, etc. Eight or nine who conducted the execution were dressed in boiler suits and wore surgical gloves. All were IRA or former IRA members."
The peer alleged: "It took almost half an hour for Paul to die. Every major bone in his body was broken. During the execution, he cried for mercy.
"Dark clouds still remain not too far from the centre of political life in Northern Ireland. Terrorism of all types has not gone away, even if it has been much reduced."
No one has yet been charged with the murder but the PSNI's deputy chief constable, Paul Leighton, said recently that most of the suspects come from north of the border.
In his Lords speech, Lord Laird alleged a subsequent meeting had taken place in south Armagh on November 2, at which a "trusted lieutenant" had spoken on Slab Murphy's behalf.
"To quell local discontent and under pressure from the top, Slab offered to put a large amount of cash into the Cullyhanna area, with the hope that buying people off with blood money would stop the rift between republicans in south Armagh.
"Their involvement in the planning, commissioning and now cover-up of this murder means that the republican leadership in south Armagh is directly implicated.
"Slab also ordered that no one in the community was to speak to the gardaì or the PSNI. He was taking full responsibility for the incident because it was his close associates involved."
Lord Laird claimed: "Having felt they had to blame someone, on Friday 9 November, six armed IRA men went to the home of Vincent Traynor. They forced their way in, but Vincent was not there."
Mr Traynor was "now considered to be the number one on the IRA hit list", he said, because he had "talked the leadership in south Armagh into a situation which saw the brutal and savage murder of Paul Quinn".
