A criminal investigation into the alleged murder of an IRA commander by two soldiers has been unable to find or question two undercover policemen who may have opened fire during the incident, lawyers have disclosed.

Codebooks to identify the unnamed officers from earlier witness statements are believed to have been lost since the 1972 killing of Joe McCann, meaning prosecutors have been unable to identify them.

At least one of the Royal Ulster Constabulary officers was seen to draw his weapon before the shooting, the lawyer for the soldiers has claimed, meaning they could have fired the fatal shots. Another soldier involved in the incident has since died.