A retired police officer who shot an IRA man 27 years ago was allegedly asked to lie if questioned about events after the killing, the High Court has heard.
He claims the request came from more senior colleagues following the death of Colum Marks - but that he would have told the truth if ever interviewed.
Details emerged during an ongoing legal bid to secure an immediate Police Ombudsman investigation into the fatal shooting.
Relatives of Marks want an order compelling the provision of funding to enable the watchdog to examine the circumstances amid claims of a shoot-to-kill policy.
The 29-year-old IRA man was fatally wounded in disputed circumstances in Downpatrick, Co Down in April 1991. Police said they believed he was armed and refused to stop during an attempt to arrest him.
But the dead man's family and legal representatives insist he was carrying no weapon at the time. They also claim police had advance knowledge of an IRA operation in the area and could have detained him.
In 2016, the Ombudsman's Office announced it was to investigate the killing following the emergence of a new eye-witness. But fresh proceedings have been brought against the watchdog, the Northern Ireland Office and the Department of Justice over a failure to provide funding necessary for the probe to get underway.
Counsel for the family, Hugh Southey QC, told the court Marks was allegedly shot in the back.
Based on newly obtained forensic evidence, he said: "We are in a position where there's a strong prima facie case that the deceased was unlawfully killed."
Mrs Justice Keegan also heard the ex-RUC man who fired the shots, referred to as Officer B, was allegedly asked by "superior officers" to lie if questioned.
However, a lawyer representing the Ombudsman insisted the alleged approach did not relate to the shooting itself.
Following submissions the case was adjourned to June.
Outside court a lawyer for the Marks family, Gavin Booth claimed: "New forensic evidence now exists which shows credible evidence of murder and this should investigated immediately."