Seamus Kearney's lawyers claimed he was wrongly found guilty of killing John Proctor on the basis of DNA found on cigarette butts recovered from the scene.But the Court of Appeal dismissed his challenge after ruling that the non-jury trial judge was entitled to conclude the stubs were smoked and discarded immediately prior to the shooting.Kearney, 57, of Gorteade Road, Maghera, Co Londonderry, was sentenced to at least 20 years in jail last December for the murder carried out in September 1981.Mr Proctor, a 25-year-old RUC reserve constable, was shot dead by the IRA minutes after visiting his wife and newborn son at the Mid Ulster Hospital in Magherafelt.Kearney had denied murder and possessing an Armalite AR15 rifle.But a judge found him guilty after hearing key evidence that his DNA profile was on a cigarette butt found among spent bullet casings at the scene.He was held to be either the gunman, the driver of a Ford Escort RS200 used by the killers, or an occupant of the car present to provide support.Even though Kearney is expected to serve only two years of his jail term under the terms of the Good Friday Agreement, he mounted a challenge to both the conviction and sentence.The prosecution argued that his refusal to enter the witness box during the trial strengthened its case that he had no innocent explanation for the DNA match.Appealing the conviction, defence counsel questioned the evidence said to show the two retrieved cigarette ends were discarded at the time of the shooting, rather than some significant period beforehand.It was contended that a description of the butts as being clean and fresh, given in evidence by a police constable who seized them, was accepted without any notebook entry on their condition at the time of recovery.But Mr Justice Weatherup, sitting with Lord Justices Girvan and Coghlin, held that there was nothing inconsistent with the cigarette ends having been discarded immediately prior to the shooting."He (the trial judge) was entitled to find the appellant's DNA arose from the appellant smoking the cigarette and then discarding the butt in the car park," Mr Justice Weatherup said.Backing the decision to admit Kearney's later conviction for possession of a rifle used in a gun attack on a UDR patrol in 1982, the court held that it demonstrated probative force.Kearney's failure to offer any alibi for the DNA find was also properly used to draw an adverse inference, according to the three judges.Mr Justice Weatherup said: "There was no basis for concluding that the passage of time would have prejudiced the appellant in offering an innocent explanation."We are satisfied that the appellant's convictions are safe. The appeal is dismissed."Kearney, who appeared via a video-link with prison, showed no emotion as his challenge was thrown out.