TIA Sharp's blood was found on a belt belonging to Stuart Hazell, the Old Bailey heard today.
Her DNA was found in two blood stains on a belt found inside a bag Stuart Hazell was carrying when he was arrested, the court heard.
The schoolgirl's body was found in the loft of the home Hazell, 37, shared with her grandmother in The Lindens, New Addington.
DNA expert Daniel Beaumont told the court there was "a one in a billion" chance that the DNA belonged to somebody else.
The first sample was on the inner surface of the belt.
Mr Beaumont said: "In my opinion the majority of the DNA in that sample had originated from just two persons.
"It was found that both Stuart Hazell's and Tia Sharp's DNA profiles were both fully represented within that profile in a manner I may expect that they both contributed DNA to that sample.
"In addition the majority of the DNA in that sample would be accounted for by a mixture of their DNA.
"I understood that the belt had been worn by Hazell and therefore I assumed he had contributed part of the DNA to that sample.
"I then considered two views: firstly that the majority of the DNA in that sample had come from Mr Hazell and Tia Sharp, and secondly that the majority had come from Mr Hazell and a female unrelated to Tia Sharp.
"And it is my opinion that it is a billion times more likely that the first view were true rather than the second."
Hazell denies murder and claims Tia accidentally fell down the stairs and broke her neck.
The second sample was found on the outer edge of the belt.
Mr Beaumont said: "In my opinion the majority of the DNA in that sample had oroingated from just one person who formed a full DNA profile which matched Tia Sharp's DNA profile.
"Therefore that DNA has come from Tia Sharp or from another person with the same DNA profile as her.
"It is estimated the probability of obtaining those profiles if the DNA had come from someone unrelated to Tia Sharp is in the order of one in a billion."
He added that the stain on the inner surface of the belt had come from "the surface of the belt had come into contact with another surface wet with Tia's blood."
He added: "It could have been Tia sharp herself, contact with a hand bearing her blood, or indeed any other surface with her blood."
Mr Beaumont also gave his opinion on a broken bracelet belonging to Tia.
Hazell had claimed Tia had "snagged or caught the bracelet on furnishing in the kitchen at the address," the court heard.
Mr Beaumont said: "In my opinion the bracelet had been damaged as a result of the bracelet having been pulled apart.
"There was no clear indication the bracelet had been cut.
"It should be noted it was not possible to determine whether the damage had been caused as a result of some deliberate action or accidental, and it was also not possible to determine how recently it had been caused."
Under cross examination, Mr Beaumont agreed that a swab of a blood stain might pick up samples previously deposited.
The trial continues.
(Story by Rachel Millard)
