DNA matching that of the man accused of strangling Elaine Doyle was found on her naked body - but not on her clothes.

Forensic scientist Pauline McSorley told a trial yesterday - the 28th anniversary of the Greenock teenager's death - it was more than a billion times more likely that the DNA profile she found came from John ­Docherty than from any ­other unrelated male.

She agreed that sweat or droplets of saliva deposited as a perpetrator strangled the 16-year-old girl could ­account for her findings.

Mrs McSorley, 57, said she and her colleagues examined tape which had been laid across Elaine's body in the hope of trapping hairs or fibres which might help track down her killer.

The forensic scientists also tested the teenager's clothes for clues.

The High Court in Edinburgh heard how some tiny traces matched the DNA of police who had handled clothing or the body, forensic scientists, and a member of the laboratory staff.

But two results could not be accounted for until ­Docherty volunteered a sample of his DNA in May 2012 and gave another sample on March last year, when he was arrested and charged with the murder.

The trial heard that the DNA on Elaine's back was an exact match.

DNA on the girl's face also matched Docherty's profile. Mrs McSorley said it was 560,000 times more likely it came from the accused than any other unrelated male.

She told the trial that if the male DNA on Elaine's back had got there as she socialised at a disco in Greenock's Celtic Club or later in the town centre, she would have expected to recover DNA from the blouse - but didn't.

Advocate depute John Scullion, prosecuting, said a pathologist had suggested Elaine was strangled from behind.

Mrs McSorley told him: "I would expect DNA on ­exposed areas closest to the perpetrator.

"That would be the back, for example."

Docherty, 49, now of Dunoon, denies murder and claims that at the time he is alleged to have stripped and strangled Elaine Doyle, 16, he was with his parents - who are no longer alive.

The trial continues.