Sinn Féin President Gerry Adams has urged anyone who knew about Robert McCartney's killing two weeks ago in Belfast to pass that information on.
The West Belfast MP also launched a scathing attack on those who carried out the stabbing, and stressed that his party supported the victim's family in their search for justice.
Mr McCartney, 33, was fatally stabbed during a fight at Magennis's Bar in Belfast. His sisters claim some IRA members were involved.
Durkan cites IRA menaces
SDLP leader Mark Durkan has said IRA menaces are preventing witnesses to the killing from coming forward.
Detectives have questioned several men, but no one has been charged with the killing.
Mr Durkan said we could not have what he described as a 'Sopranos culture' where IRA bosses are above the law.
Mr Durkan is travelling to the United States this week where he said he intends to brief the US Special Envoy, Mitchell Reiss, on Mr McCartney's killing.
