The sisters of Robert McCartney, murdered outside a Belfast bar last year, have begged for those with information to come forward.
Twelve months after the knifing of Mr McCartney and his friend, Brendan Devine, they appealed for the occupants of a blue car seen in the vicinity of the attack to tell police what they saw.
At a joint press conference with the family, Det Insp Phil Marshall said those travelling in the car could have witnessed the killing as it waited at traffic lights near Magennis's bar where the dead man had been drinking.
The sisters and partner of the 33-year-old father of two yesterday begged for new information to be given to the police so they could end their grief.
Paula McCartney 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."
Referring to the police call for fresh information, she added: "The blue car is very significant. We would appeal directly to the person or persons in that car to please search their hearts and tell what they know."
Det Insp Marshall 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."
"Robert and a number of other people were on the road in front of that vehicle. We believe the occupant or occupants of that car were aware of something happening on the road directly in front of them."
The car's occupants may have thought that they were witnessing a violent, drunken struggle, he said. "But it's important that they are aware that this was an attack that led to the murder of Robert McCartney."
He added: "We believe the occupants may have revved the engine of the car when traffic lights turned green. This may have been an indication to people in front of them to move off the road."
Information from the driver or other people in the car could prove to be really valuable to the investigation, he added.
The McCartneys and Bridgeen Hagans, mother of the dead man's children, claim the IRA has been shielding those responsible for the murder. They further allege they have been intimidated and that the facts surrounding the killing have been deliberately withheld from the PSNI.
Following the murder Sinn Féin suspended 12 of its members and called on witnesses to come forward to the police.
The IRA denied involvement but later claimed it had expelled three of its men, and even offered to shoot those responsible.