The family's campaign took them from the Short Strand to the White House
By Vincent Kearney
BBC NI home affairs correspondent
When father-of-two Robert McCartney was stabbed to death outside a Belfast bar, it was a gruesome ending to a life that had been lived in the nearby Short Strand, a staunchly republican enclave in the east of the city.
Within hours of his killing it was claimed that IRA members had been involved after a fight in Magennis's, a pub in Belfast city centre on the night of 30 January 2005. Sinn Féin rejected those claims.
The killing came at a crucial time for the party, when it was involved in delicate political negotiations aimed at securing its support for the police.
Terence Davison, 51, was cleared of murdering Robert McCartney
Robert McCartney's family accused republicans of hindering the murder investigation by covering up what happened, and threatening witnesses.
There were about 50 people in the pub on the night of the killing, but none appeared willing to tell the police about what they saw.
The trial exposed the extent of the IRA's influence in many working-class nationalist areas like the Short Strand.
Many were clearly afraid of the consequences, but Mr McCartney's sisters were not.
They mounted a high-profile campaign that took them from the streets of the Short Strand to the White House, and even to Sinn Féin's ard fheis in Dublin.
Finger of blame
They relentlessly pointed the finger of blame at members of the IRA.
Eventually, it became clear that IRA members had indeed been involved in the Robert McCartney killing in Market Street, a narrow side street beside the pub.
Sinn Fein announced that it had suspended seven members of the party who were in the pub on the night of the murder, and the IRA even offered to shoot those responsible.
Witnesses eventually came forward and in June 2005, 51-year-old Terence Davison was charged with murder.
It was alleged that the fight in Magennis's had started after Robert McCartney made a rude gesture to his wife.
Two other men, Jim McCormick, 39, and 47-year-old Joseph Fitzpatrick, were charged with affray.
Their trial at Belfast Crown Court exposed the extent of the IRA's influence in many working-class nationalist areas like the Short Strand.
One of the witnesses was Brendan Devine, who was Robert McCartney's best friend and was with him and was stabbed on the night of the killing.
He told the court that he met the IRA four times afterwards, with the first meeting taking place in Sinn Fein's offices on the Antrim Road.
Another witness, Ed Gowdy, told how he was visited by IRA members even before Mr McCartney had been buried.
He was visited again a number of times by representatives of the IRA's Army Council.
Both witnesses said they had only co-operated fully with the police after being given clearance by the IRA to do so.
But it was an unidentified woman who was driving into Belfast on the night of the killing who was the key to the prosecution case.
Referred to as Witness C, she stopped at traffic lights at the end of Market Street and said she saw Terence Davison attacking Mr McCartney from just five feet away.
The prosecution argued that she witnessed the fatal stab wound, but there were problems with her description.
The witness said the man she saw attacking Robert McCartney had shocking white-grey hair that was straight and came down to beneath his ears.
The killing followed a row in a bar
However, photographs taken from CCTV cameras just 25 minutes after the murder showed Terence Davison with much shorter hair, and the clothes he was wearing did not fit the description given by Witness C.
There were also differing accounts of where the stabbing took place.
Brendan Devine told police that it happened about two thirds of the way along Market Street, a location that could not have been viewed by Witness C from her parked car.
But in court he changed his story and said it could have happened at the end of the street where Witness C said she saw the attack taking place.
He rejected suggestions that he deliberately changed his story to make it dovetail with Witness C, and said he may have initially got the location wrong because he was confused after being stabbed.
None of the defendants entered the witness box during the month-long trial and the judge ignored a suggestion from the Crown that he should draw adverse implications from that.
The defence barrister, Orlando Pownall, said the "extraordinarily diverse" evidence given by the Crown witnesses "exposed the shortcomings'' in the prosecution case.
It was on these key points that the trial turned. The judge, Mr Justice John Gillen, praised the evidence of Witness C but ultimately could not rely on it.
He said she was "transparently honest" and courageous to give evidence, but he said he found flaws in that evidence and was not satisfied beyond reasonable doubt that she had seen what she believed she had seen.
For the McCartney family it's been a long journey, from the Short Strand to Dublin, Downing Street and the White House and it's a journey that for them is not yet over.
Speaking after the verdict, Mr McCartney's sister Catherine, spoke with characteristic determination.
"We have been carrying a cross for three and a half years and we're still carrying it and we will go on carrying it."