World's End murders: Components of Angus Sinclair's DNA found on tights
The World's End murder trial has heard DNA from a torn pair of tights used as a ligature matched components of the accused's profile.
Angus Sinclair, 69, denies raping and murdering 17-year-olds Helen Scott and Christine Eadie in October 1977.
Forensic scientist Geraldine Davidson was giving evidence about samples from the teenagers' clothing used as ligatures on the girls.
New techniques mean samples that have degraded can now be analysed.
Mrs Davidson agreed with the Lord Advocate, who is prosecuting, that it was possible Christine Eadie's tights had been ripped into ligatures and used to bind her wrists and neck.
She said she would be looking for DNA in areas around rips and tears, as it would require some degree of force to do this and it was likely to have been handled.
The court also heard about a knotted area of another part of a ligature from Christine's neck.
Mrs Davidson said she was interested in the area of the knot as she wanted to "try to detect DNA for the person who tied the knot."
She said a mixture of DNA profiles of Mr Sinclair and his brother-in-law Gordon Hamilton were found on it.
The conclusion from an expert statistician was that there was extremely strong support for both Gordon Hamilton and Angus Sinclair being contributors of the DNA and it was over a billion times more likely to have come from them than either or neither of them.
Mr Sinclair blames his brother-in-law for the teenagers' murders.
Ms Eadie's body was found the following afternoon at Gosford Bay, Aberlady, while Ms Scott's body was discovered a few hours later in a wheat field near Haddington.
Mr Sinclair has submitted three special defences of incrimination - blaming his late brother-in-law Gordon Hamilton; one of alibi - saying he was fishing on the banks of the Firth of Forth near Cockenzie power station at the time; and that the two girls consented to sexual intercourse.
Mr Sinclair is alleged to have gagged the girls, bound their wrists and tied a ligature around their necks.
He denies inflicting blunt force injuries on Ms Eadie by repeatedly punching and kicking her on the body and biting her.
He also denies forcing Ms Scott to walk barefoot into a field, ripping the strap from her handbag, repeatedly punching and kicking her on the head and body and stamping on her head.
And he denies stealing clothing, footwear, jewellery and other personal effects from the teenagers in an attempt to pervert the course of justice.
The trial at the High Court in Livingston continues.