A threatening letter that the McCartney sisters and Robert McCartney's partner, Bridgeen Hagans, received on their return from the US has been handed to the PSNI for forensic examination, the police have confirmed.
The letter was among several letters of support that were sent to the home of Ms Hagans, the fiancée of Robert McCartney who was fatally stabbed in an incident outside Magennis's pub involving some senior IRA members over seven weeks ago.
The family has complained of a "whispering campaign" against them and a "wall of silence" that is preventing Mr McCartney's killers being convicted in court.
A spokesman for the family said the letter upset Ms Hagans and the sisters. He said the letter referred to the family being on a "hit list", to "bullets being too good for them" and to a threat of members of the family facing a potential knife attack, similar to the attack that killed Mr McCartney.
Meanwhile, Taoiseach Bertie Ahern said last night that incidents allegedly involving the IRA such as the murder of Mr McCartney, the £26.5 million robbery from the Northern Bank, and IRA multi-million pound money laundering cannot be allowed to continue.
Mr Ahern in interviews with the BBC, UTV and Channel 4 spoke on the current issues that have caused a crisis in the peace process and prompted the McCartney family to embark on their "Justice for Robert" campaign.
The Taoiseach said people who had witnessed the murder must come forward and deliver usable testimony.
"We need sooner rather than later - and that is very soon - evidence that can lead to prosecutions and convictions. Clearly there are people who can assist in that. This was not a murder in a back lane without witnesses," he said.
"There has to be clear evidence that can be used and that can be procured by the police in a way that they can stand it up.
"We all know in the rule of law you have to prove something, and the only way to prove it is based on facts, and there are people who have those facts," added Mr Ahern.
The Taoiseach said a way out of the current crisis was the IRA ending all activity and decommissioning and Sinn Féin embracing policing. He said the security assessment remained that some of the money recovered in Garda raids last month was part of the Northern Bank robbery, although gardaí have yet to officially confirm this.
Mr Ahern said he believed that Sinn Féin president Gerry Adams was working to deliver the implementation of the Belfast Agreement and a democratic peace "otherwise I would not be talking to him".
With sources indicating that the British and Irish governments may be prepared to make another drive for a comprehensive agreement in September, Mr Ahern said that the Government's commitment to the current phase of the peace process would not continue indefinitely.
"What we want to see - and what we are not sure of, quite frankly - is it within the ability of Sinn Féin to bring to be able to bring that across the line? Time is running out and it won't go on endlessly, I can assure you of that. We have made it very clear over the last two years that this can't go on on a never, never basis," the Taoiseach added.
Mr Ahern also said the British government had reneged on the Belfast Agreement by failing to deliver a public and independent inquiry into the murder of Belfast solicitor Pat Finucane.