Relatives of Denis Donaldson have rejected claims that the Provisional IRA was responsible for his murder or that Gerry Adams authorised the killing.
The former Sinn Féin official was killed in a remote cottage in Co Donegal in 2006, months after admitting having worked as a spy for British intelligence for more than two decades.
A BBC Spotlight programme earlier this week carried allegations by a man claiming to be a former Special Branch agent that the IRA killed Mr Donaldson and Mr Adams would have sanctioned it.
Ciaran Shiels, a lawyer representing the Donaldson family, said yesterday the claims "just do not stand up".
He told the BBC: "The theory that was being advanced by BBC Spotlight earlier this week, that this was in some way carried out by the Provisional IRA or authorised by Gerry Adams, I think it's absolute nonsense.
"It does not marry in any way with the lines of inquiry that have been progressed by the Garda or by the the police ombudsman."
Mr Adams has denied any involvement in the murder, and has said he is considering suing the BBC over the broadcast.
Sinn Féin MLA Gerry Kelly last night said the comments by Mr Donaldson's family prove that the allegations are without foundation.
"The reality is that anti-peace process republicans claimed responsibility for the killing of Denis Donaldson in the full glare of the media. That has been the line of investigation pursued by Garda for the last 10 years."
BBC Spotlight said: "The Spotlight programme dealt with matters of great public interest and the BBC stands by its journalism."
