Forensic scientist Martin Fairley examined staining on Helen Scott's coat.
Angus Sinclair, 69, denies raping and murdering teenagers Helen Scott and Christine Eadie in October 1977.
The trial at the High Court in Livingston continues.
Sinclair's special defences are incrimination - blaming his brother-in-law Gordon Hamilton, who is now dead; 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 World's End murder trial has heard a DNA sample on the clothes of one of the victims has one in a billion chance of coming from a person other than the accused.