Advocate depute John Scullion, prosecuting, sug-gested the naked girl was strangled from behind by a man who had previously been speaking to her.
Her body was found near her home in Ardgowan Street, Greenock, in June 1986.
John Docherty, 49, now of Hunters' Quay, Holiday Village, Dunoon, denies murdering the 16-year-old and claims that at the time he was with his parents at their home in Anne Street.
The trial at the High Court in Edinburgh has heard that some 20 years later, sticky tape used to try to recover hairs and fibres from the dead teenager's skin had yielded traces of DNA from "an unknown male" on Ms Doyle's back. Tiny traces of DNA on her face probably came from the same man, said forensic scientist Terence Randall.
Yesterday, Mr Scullion put to him: "While naked, Elaine Doyle was strangled with a ligature by a male positioned behind her."
Mr Randall agreed that, if that were the case, he would expect to find the killer's DNA on the girl's back.
Mr Scullion continued: "If the perpetrator was exerting himself physically in order to strangle Elaine Doyle with a ligature, could that result in a transfer of DNA?"
Mr Randall agreed that it could. DNA might come from sweat or breath.
Mr Docherty also denies stealing a handbag on the same date and attacking another woman between 1990 and 1995.
The trial continues.