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President Bush told the family of slain Irishman Robert McCartney (search) that he would do whatever he can to help bring his killers to justice, his sisters said after a St. Patrick's Day (search) meeting with the president in the White House.

McCartney was beaten and stabbed to death outside a Belfast pub on Jan. 30. His family blames the outlawed Irish Republican Army (search) for his death and is calling for charge of her brother's death and said he supports their cause, although he didn't say exactly what he would do to help.

"We pressed on the president the importance of getting justice for Robert, and he said he's 100 percent behind our campaign," Catherine McCartney said, standing outside the White House gate with the rest of her sisters and her late brother's fiancee. "We believe very much that Ireland as a whole and the peace process require justice for people back in Ireland and that he was 100 percent behind us."

The sisters are hoping that public support in the United States for their cause will spur Sinn Fein (search) and the IRA to encourage witnesses to offer evidence directly to Northern Ireland's police force. The Sinn Fein-IRA movement, which rejects police authority, instead has advised witnesses to offer statements to lawyers, a widely criticized policy in Northern Ireland.

Before meeting with the McCartneys, Bush received a bowl of shamrocks in a public ceremony with Irish Prime Minister Bertie Ahern (search). Bush pledged to help the Irish people move toward a lasting agreement in Northern Ireland peace process.

"As you work for peace, our government and the American people will stand with you," Bush said.

Because of the allegations about the IRA's involvement in McCartney's death and a bank heist on Dec. 20, Bush did not invite Northern Ireland political leaders who attended for 10 years, including Gerry Adams, head of Sinn Fein, the legal political arm of the IRA.

"There is no place for the violence and the thuggery and the criminality," White House press secretary Scott McClellan said of the IRA. "The president made that clear."

Ahern said renewed power-sharing in Northern Ireland between Protestant leaders and Sinn Fein, the major Catholic-backed party, required the IRA to deliver "a definitive closure to paramilitary capability and activity, including all forms of criminality."

Ahern spoke to Adams for an hour Wednesday night. He said the Sinn Fein leader faced deepening isolation, particularly in Washington, unless the IRA goes out of business.

"People want to see that we're going to get action, because if we don't, let's be frank about it, the icy reception this week will turn in to just total exclusion, which is the opposite of what we want to achieve," he said. "If we don't see action, I'm not too sure I want to be around next year."

Not welcome at the White House, Adams was met with a standing ovation Thursday morning as he spoke to supporters at a Washington hotel. Adams told Friends of Sinn Fein that neither the McCartney killing nor the cold shoulder from some U.S. officials would weaken his party.

"We who would not allow the British government to criminalize us, we will also not allow any rogue elements on the fringes of Republicanism to criminalize our struggle," said Adams.