The family of Robert McCartney have said that Sinn Féin's conduct since the killing has been even more hurtful that the killing itself.
The 33-year-old died after being stabbed outside Magennis's bar in Belfast city centre on January 31 last year.
The IRA later offered to shoot members believed to have been involved.
After the killing Sinn Féin suspended seven party members and the IRA expelled three of its members.
But two of Mr McCartney's cousins have now hit out at Sinn Féin, whose support, they say, "lay with the people involved in Robert's murder, not with the McCartneys".
The charge has been rejected by Sinn Féin.
Last May Terence Davison and James McCormick were charged with murdering Mr McCartney and attempting to murder Brendan Devine.
But the McCartney family remain convinced more people should face the courts.
In separate letters to The Irish News Gerard Quinn and his sister Kathryn accused "democratically elected republican representatives" of "using their positions to manipulate opinion on the facts".
Mr Quinn said rioting which followed police searches in the Markets area of south Belfast after the killing was "an orgy of allegedly orchestrated violence aimed at hindering the investigation".
"Alex Maskey Sinn Féin MLA for South Belfast the scene of the disturbances publicly stated that 'the scale and approach' of the police operation was completely 'unacceptable and unjustifiable'," he said.
"Mr Maskey's comments angered not just the murdered man's family but also the local community and saw an unprecedented uprising within republicanism."
Kathryn Quinn said the pain of losing her cousin had got worse in the past year.
"What in my opinion has to be the worst was the lack of support despite proclaiming the opposite from Sinn Féin, a party we had voted for and people we had known and respected for many years," she said.
Sinn Féin's Gerry Kelly said the party had "made very clear our determination to help the McCartney family".
"The party has clearly and unambiguously repudiated those who were responsible for Robert McCartney's murder," he said.
"The party president has repeatedly called on everyone with information to make it available. We have worked hard on the ground to create the climate in which this can happen.
"Witnesses have come forward and made statements... Indeed the PSNI confirmed in May that they had received 151 witness statements. This does not square with the allegation of a wall of silence."
Mr Quinn appealed to the "at least 45" independent witnesses he believes were in Magennis's bar on the night of the killing to come forward.