The McCartney family last night said the IRA was still protecting the people who killed their brother outside a Belfast city centre pub.
Catherine McCartney and her sister Paula were in Kerry to address the annual conference of the Labour Party.
"The central message is that the IRA are still protecting people who murdered Robert and that is the reason why there have been no arrests," said Catherine McCartney.
It is now four months since Robert McCartney was beaten and stabbed to death outside Magennis's bar in Belfast. Ms McCartney said the IRA had initially wanted to protect all of their members but had then decided after the wave of international pressure to allow some to face minor charges.
"We believe there were 15 people involved and that the key republican is still being protected," she said. Ms McCartney said it was natural that media interest in their campaign for justice would dwindle but added that the actions of politicians and police were more important.
"We can't just rely on the media. It's political leadership that is needed to resolve this. And we're in close contact with people in Europe, America and obviously here in Ireland," she said.
Last week, the family received threats from republican elements. "Republicans have allowed this to go on by encouraging this perception that we are damaging the republican movement - when the only people damaging it are the people who murdered Robert," said Ms McCartney.