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A Sinn Fein leader publicly criticized the family of a Catholic man killed by IRA members, warning Monday that their relentless drive for a conviction in his death could diminish support for their cause.

The comments from Sinn Fein's deputy leader, Martin McGuinness (search), came as the party admitted that another of its candidates was in the pub where Irish Republican Army (search) members launched the fatal assault on Robert McCartney (search).

A campaign by McCartney's five sisters to have his killers brought to justice has focused attention on the outlawed IRA's continued grip on hard-line Catholic parts of Belfast, where telling police about IRA activities can mean a death sentence.

Catherine McCartney, one of the sisters, on Monday accused Sinn Fein (search) of continually trying to conceal and downplay its members' role in the attack.

"I find it hard to believe that we've been campaigning for six weeks and still not a single person has been charged with Robert's murder," she said in an interview in her sister Paula's home in Short Strand (search), an IRA power base that is home to several of the IRA figures who allegedly attacked their brother.

But McGuinness, an alleged IRA commander, said in what were Sinn Fein's first publicly critical comments of the family: "The McCartneys need to be very careful. To step over that line, which is a very important line, into the world of party-political politics can do a huge disservice to their campaign."

He said if they continued to make direct challenges to Sinn Fein, which is the largest Catholic-backed party in Northern Ireland, they would "dismay and disillusion an awful lot of people, tens of thousands of people who support them in their just demands."

The IRA-linked Sinn Fein, which has already suspended seven members linked to McCartney's death in January but identified none of them, admitted that a Sinn Fein candidate for May's election to Belfast City Council was in the bar. The candidate, 23-year-old Deirdre Hargey (search), issued a statement Monday.

"I did not witness the fracas in the bar, or the incident outside the bar," she said.

On Saturday, Sinn Fein said a candidate in Northern Ireland's 2003 legislative elections, Cora Groogan (search), 23, was also in the bar. Groogan issued a statement claiming she heard "commotion" but saw nothing.

The IRA has admitted that two of its members slashed McCartney's neck and stomach after he intervened in a dispute at the pub Jan. 30. The 33-year-old man died hours later.

Catherine McCartney said the neighborhood's IRA chieftain, who allegedly ordered henchmen to attack her brother, was seen at a local shop last weekend. The man who knifed her brother to death, she said, was spotted in local pubs.

"Everybody knows who killed my brother, and who ordered it, but they're still strutting about the place like they own it," she said. "The fact is, Sinn Fein keeps saying they want people to give evidence. But here we have two examples where Sinn Fein people are playing deaf, dumb and blind."

Paula McCartney stressed that the family included longtime supporters of Sinn Fein and the IRA and did not have an anti-Sinn Fein agenda.

"Our family did not hatch a plan to harm Sinn Fein," she said. "We're a republican family."

All five McCartney sisters and their brother's fiancee are scheduled to meet President Bush at the traditional St. Patrick's Day reception at the White House on Thursday.

Sinn Fein leader Gerry Adams (search), who has been part of the White House celebration for years, has been barred from official U.S. government functions this year.

During their trip to the United States, McCartney's sisters are expected at some social functions to bump into Adams, a reputed IRA chief.

Adams met the McCartneys last month and reassured them he would press for witnesses to come forward, but Catherine McCartney said she probably would not shake his hand.

"He seemed genuine when he met us, when we thought the problem was just a matter of IRA intimidation," she said. "Now we know better. It's clear that Sinn Fein is heavily into the cover-up."