Sinn Féin has rejected claims that it has not done enough to help the family of murdered Belfast man Robert McCartney.
Mr McCartney was killed a year ago and his family have made a new appeal for information.
His sister Paula said they had not been shown the results of internal investigations carried out by Sinn Féin and the IRA and asked why these could not be passed on.
However, Sinn Fein's Chief Negotiator, Martin McGuinness, claimed the party had done everything in its power to assist the McCartney family.
Speaking at a press conference on the first anniversary of the killing, the McCartney family urged the driver of a mystery blue car to help end their year of torment and bring his killers to justice.
The PSNI has made a new appeal over the vehicle they believe was stopped at traffic lights near the scene of the Belfast city centre stabbing.
Paula McCartney insisted the pain and trauma would not ease until the gang members responsible were all caught.
She said: 'Our grieving process has been hindered by the fact that the people who took his life for no reason at all have not been held to account. We also believe if we had some closure by these people being brought to justice it would help in the grieving process of this family.
'We are practically begging people, please, if they have any information at all, release it and put this family out of the misery they have been suffering for a year.'
PSNI Detective Inspector Philip Marshall urged the occupants of the large blue car, make and model unknown, that was driving through Belfast city centre on the night Mr McCartney was killed to consider the possible significance of what they saw.
He said: 'The driver or occupants of this large blue car may not realise what they were seeing was an attack in which Robert was killed.'
Police have studied CCTV footage of two potential routes the vehicle took on the night, including at one point being on East Bridge Street waiting to turn on to Victoria Street.
Detectives believe the car stopped at a red traffic light for up to 70 seconds near where the violent struggle was taking place.
Mr Marshall added that Robert and a number of other people were on the road in front of that vehicle.