The blood of a missing businesswoman was discovered at a flat where she was allegedly tortured and killed, a court heard.
Forensic scientist Nighean Stevenson, 40, said DNA taken from a spot of blood on the bathroom floor matched that of Lynda Spence.
The 27-year-old disappeared from Glasgow in April 2011 and four men stand accused of abduction and murder.
Prosecutors claim the financial adviser was tortured for up to a fortnight at the home of accused David Parker, 38, in West Kilbride, Ayrshire.
Ms Stevenson, from the Scottish Police Services Authority, was called to examine the property in October 2011 and took a swab of a blood spot found on the bathroom's linoleum floor at the base of the bath.
She told the jury at the High Court in Glasgow: "The blood was analysed and a profile was obtained that matched the DNA profile of Lynda Spence."
The expert said the chances of the blood coming from any other person were "one in one billion".
Parker, Colin Coats, 42, Philip Wade, 42, and Paul Smith, 47, deny murder.