The World's End murder trial has been hearing how semen found on two dead girls shared the same DNA profile.
Helen Scott and Christine Eadie went missing in 1977
Angus Sinclair denies raping and killing Christine Eadie and Helen Scott, both 17, in 1977 after a night out at Edinburgh's World's End pub.
Forensic scientist Martin Fairley said the tests were carried out in mid-1995 using the latest profiling techniques.
However, he told the court they could only narrow the DNA profile down to one in 2,400 of the male population.
Mr Fairley, 45, said tests then known as STRs for "Short Tandem Repeats" or "Quads" only examined four areas of DNA compared with the 10 areas examined today.
He described how Christine's blood could not give a DNA profile because it had been kept too long. But a result was obtained from her hair.
DNA was also extracted from a vaginal swab which had a different profile.
The scientist described how similar tests had been carried out on semen found in Helen Scott.
"This DNA profile matches the sample taken from Christine Eadie's vaginal swab," Mr Fairley told the trial.
Stains on the coat which was found thrown across Helen Scott's partially clothed body were also examined and again the DNA matched, the court heard.
The coat has been tested several times over the years as advances were made in forensic technology.
The girls were last seen alive at the World's End pub
Detective Constable Andrew Ritchie, 45, told the trial that on November 25 2004 he had detained Angus Sinclair and taken a mouth swab.
On 31 March the following year, Mr Sinclair was formally arrested and charged with the World's End murders.
Mr Sinclair denies raping and murdering the 17-year-old girls.
He claims that any sexual contact with the girls was with their consent and that his brother-in-law, Gordon Hamilton, was the killer.
Mr Sinclair is alleged to have driven Miss Eadie to Gosford Bay, Aberlady, and there or elsewhere she was attacked, stripped and gagged with her underwear.
Mr Sinclair is accused of tying her wrists and neck, raping her and killing her by restricting her breathing.
He is accused of raping and murdering Helen Scott in the same way and driving her to a road near Haddington and, in a field there or elsewhere in Edinburgh and East Lothian, attacking her.