The US has pledged its support for the campaign to bring the killers of Robert McCartney to justice.
President Bush's envoy to Northern Ireland, Mr Mitchell Reiss, said after meeting Mr McCartney's sisters in Washington today that he had an extraordinary meeting with them and condemned the "terrible, terrible, terrible murder".
"I stand by all Americans in my admiration for their courage and determination to bring justice for Robert," he said.
"The United States will do everything it can to support them."
Before the meeting, the McCartney's said that failure to bring the killers to justice will send a grave message to the people of Northern Ireland.
The five sisters, who have brought their campaign to Washington, said they were determined to make it known that such brutal murders should not be tolerated. As they prepared to meet US envoy to Northern Ireland, they warned that even if a peace deal was struck, violence in Belfast would not end.
Mr McCartney's sister Catherine McCartney said: "There will still be people walking through the streets of Ireland able to kill because they belong to organisations.
"If these people are brought to account, it will be a sign to the people of Northern Ireland that law and order prevails and not men of violence."
She said the fact that the family was in the US meant that their message was already being heard by those with influence in Northern Ireland.
As they prepared for a long day of meetings with congressmen and women, her sister Paula said she was optimistic their visit would reap rewards.
"We will work hard and while we will not see a result today, hopefully inevitably we will," she said. Catherine refused to rule out running for election in May although she conceded that this may not be the best way to bring her brother's killers to justice.
"Getting these people into court is our main aim," she said. "There are always other options."
The family will meet senators Ted Kennedy and Hillary Clinton today before presenting president Bush with a detailed narrative of events surrounding their brother's murder tomorrow.
Mr McCartney (33) was brutally attacked outside a Belfast pub on January 30th and while the IRA has expelled three volunteers and Sinn Fein has suspended seven members over the attack, no one has been charged.
Meanwhile, the former US envoy to the North Richard Haas warned Sinn Féin that US patience with IRA was wearing thin.
"9/11 fundamentally changed this country and there is simply zero-tolerance in the United States for this sort of thing anymore," he said.
Agencies