After the Washington hoopla, the McCartney sisters faced a colder reception back home in Belfast. But, they tell Chris Thornton they won't be deterred from seeking justice

The church where Robert McCartney was commended unto God may not have been there at all if it hadn't been for the IRA. St Matthew's, the lonely Catholic spire in east Belfast, is where the Provisional IRA's reputation in the city was made on a June night 35 years ago, a year before Bert McCartney was even born.

When loyalists seemed ready to storm through the church that night, threatening it and its congregation in the narrow Catholic enclave of the Short Strand, the IRA fought what is still referred to as the Battle of St Matthew's. Three men died - two Protestants and a republican - but the little district wedged between the River Lagan and the greatest concentration of loyalists in the city survived.

The graffiti that derided the IRA - 'I Ran Away' - when the Troubles erupted less than a year before had been made defunct. The Provos were the defenders of the people.

The question now is whether that reputation, reinforced many times throughout the Troubles, can outlive Robert McCartney. This week the IRA attempted an answer in its fourth successive statement dealing with the events in Magennis's Whiskey Cafe on January 30, when IRA members used a knife to end a bar fight and the father-of-two's life.

Such frequency of statements is rare, if not unprecedented, but this time the IRA said it was drawing a line. It had offered to shoot the men involved, and it seems that was as far as things will go. "The IRA moved quickly to deal with those involved," it said. "We have tried to assist in whatever way we can. Unfortunately it would appear that no matter what we do it will never be enough for some." Nothing more to say. Keep moving.

The McCartney family can't agree. The IRA's expulsion of three members and Sinn Fein's suspension of seven more republicans is not enough to satisfy their sense of the justice. "Expulsions, suspensions, it sounds like something out of the classroom," says Catherine McCartney, one of the dead man's five sisters. "This is a murder inquiry. It's not being treated seriously."

So hours after returning home from the White House, Robert McCartney's sisters were back beating the drum again, asking for serious treatment from the IRA and Sinn Fein. They plan more rallies in Belfast and a trip to the European Parliament.

But after the crescendo of media attention in Washington, there is a sense in Belfast that this period may be the hard part for them, a sense compounded by a threatening letter that awaited their return. Eight weeks have passed since the murder, witnesses are still scared and goodwill loses its momentum. A boilerplate election and the marching season are starting to push for space on the public agenda.

"I think they're very articulate," says the relative of another murder victim who slipped off the headlines many months ago. "I think they've been able to highlight their case like very few people before them. But are they going to get Gerry Adams to hand people over? I don't think so, and that means there is a danger of the whole thing dying."

The McCartneys are also aware that there has been a kind of media saturation of their plight. "To be honest with you, I'm sick of hearing the name McCartney," Catherine McCartney says wearily in the middle of another cycle of coffee, cigarettes and interviews. "So I'm sure other people are fed up with hearing the name McCartney.

"But the fact is that people have to stay focused on the issue here. Robert was murdered. Seventy people who were in that bar are not talking. Why not? That is the question the people of Ireland have to ask themselves. Why are people not talking?"

The McCartneys know there is a fine line between sympathies in Short Strand, sympathies for the injustice of their loss and those bound to the IRA's legacy as the saviours of the Strand. A rally at the murder scene was suggested for this weekend, but put off because it could force people to choose between republican Easter commemorations and the family's campaign. In their first visits to the Dail and in all their political contacts, they have been careful to include Sinn Fein and listen to the party's promises of support.

But less than a month after the sisters were lauded at the Sinn Fein Ard Fheis, they seem to be increasingly drawn into confrontation with the republican movement. Jet lag after Washington cannot disguise their anger that more Sinn Fein members than initially thought were in bar at the time of the murder.

Three Sinn Fein candidates, two past and one current, have been identified as potential witnesses. They have not been suspended by the party and, in spite of Gerry Adams's earlier exhortations to help the family, they provided statements to the North's Police Ombudsman only after their identities were made public. Police sources have said the statements provided "little evidential value". Whatever they say, they say nothing.

Catherine McCartney says the notion that there is a taboo on people from republican areas dealing with police is "a smokescreen". "Who else would you deal with? Are they trying to say murder cases in Northern Ireland involving Catholics were never dealt with by the RUC in its worst days? Of course they were. It wasn't always dealt with by the republican movement.

"It just basically boils down to the fact that their members were involved. That's all this is about. They don't have any qualms about the crime itself. The IRA admitted it was a crime. Sinn Fein have said it was a crime.

"Everybody's agreed on the basic issues. Nobody's agreed on the methods of how these people should come forward or whether they should come forward or who they should come forward to. There's a reason they haven't come forward to the police or the Police Ombudsman. I don't believe all those 70 people will not deal with the police.

"You're talking - how many people are there in Ireland, five million? - and we're talking about 70 people who are holding this thing up. I mean, if I was a Sinn Fein party member or a Sinn Fein supporter, which I was, I would be asking 'why are these people afraid to come forward to talk to the Ombudsman?'

"The republican/nationalist community have to ask Sinn Fein, the way they've asked the British Establishment, what are youse hiding? Who are youse trying to protect? Why don't you want the truth to come out? That goes for everybody up to the leadership. It's up to them to think how do we break down these walls of silence."

The failure thus far to hold anyone to account for the murder, Catherine McCartney says, "is a justice issue not just for us, but the whole of the republican community".

Through the most intense periods of recent criticism, Sinn Fein supporters have consoled themselves with the notion that this too shall pass. The party will expand again in the North's May elections and, ultimately, the centre stage of politics still awaits. There will be no settlement in the North without them.

But the McCartneys say they won't go away either. If Sinn Fein returns to Stormont, they will be waiting for them, asking if political republicans will defend the people like them.

"We just keep battling," says Catherine. "If it ever does come to talks, and they do get powers of policing and justice transferred, then that will be a key lobbying point. We can say 'Now youse have the power. What are you going to do about it?'"

Chris Thornton is Political Correspondent editor of the Belfast Telegraph