The IRA killers of east Belfast man Robert McCartney are damaging the republican movement by "not doing the right thing", a former prisoner has said.
Paul Norney, who served 22 years after being convicted with four others of the attempted IRA murder of an English police officer, also claimed that given his own experience of the justice system the offer to shoot Mr McCartney's killers was "very humane".
However, the republican, who was 17 when arrested in England, stressed that he did not condone the IRA's offer, which was rejected by the victim's family.
"I don't believe anybody should be shot, dragged down an entry, and a bullet put in their head. It is totally barbaric," he said.
"But again, having experienced our justice system, that is barbaric in my view.
"My argument is we need a proper justice system.
"I don't believe they (the IRA) would have carried it through (the threat to shoot).
"It was an offer basically to say 'look we want this issue sorted out, we are with you on this issue. We disagree with what happened to your brother, this is the only way we can get you justice'...That is the only way in their terms they felt they could deal with it."
Although the IRA said it had expelled three figures and Sinn Féin also suspended several members, no-one has yet faced charges in connection with Mr McCartney's murder outside a Belfast bar on January 30.
Despite a number of arrests, the PSNI probe has been hampered by a lack of forensic evidence and witnesses prepared to testify in court.
Republicans, including the Sinn Féin leadership, have called for those in the bar to come forward, but the victim's family believe witnesses are still being intimidated.
"Even if Gerry Adams and Martin McGuinness say we want you to make statements, there is resentment, suspicion of the police and justice system they (any witnesses) just won't," Mr Norney said.
But with no breakthrough in the case, the republican said he believes the onus lies with the killers.
"I don't really have the answer as to how you mete out justice.
"If people do wrong in society, they must be punished...I think they (the killers) should atone for what they have done. They must be called to account in some way."
In a direct appeal, he added: "Do the right thing. A young man is dead who shouldn't be dead.
"He has left a family and kids behind."
"They (the killers) are damaging the republican cause as well. They need to sort it out. It is dragging on and dragging on, and is being used politically as a stick to beat the republican movement as a whole.
"They have a moral obligation to uphold the cause that they claim to be struggling for and morally they have killed a young man. They should do what they feel their conscience dictates if they are true republicans."