A police forensic expert has testified that a knife prosecutors say might have been used to kill a British student bore traces of the DNA of a US co-defendant in the murder trial in Perugia.
Amanda Knox is being tried in a Perugia courtroom for the 2007 murder of roommate Meredith Kercher in their rented apartment in the Umbrian university town.
Also on trial for Kercher's murder is Knox's former Italian boyfriend, Raffaele Sollecito.
All three were studying in Perugia. Knox and Sollecito deny wrongdoing.
Defence lawyers challenged the findings of police forensic expert Patrizia Stefanoni, who testified for the prosecution for eight hours about DNA found at the apartment.
Prosecutors have alleged that Knox's DNA was found on the handle of a kitchen knife that might have been the murder weapon, while Kercher's DNA was found on the blade of the knife, found at Sollecito's house. Prosecutors also say Sollecito's DNA was found on the clasp of the victim's bra.
The Italian news agency ANSA quoted Ms Stefanoni as testifying that traces of Knox's genetic code were found in a small scratch on the knife's handle, and that the point in which the genetic material was found indicates that the knife "was used to pierce and not to cut".
Prosecutors allege Kercher was stabbed during what began as a sex game.
The trial began in January for Knox and Sollecito, who risk receiving Italy's stiffest punishment, life imprisonment, if convicted of murder. They are also accused of sexual violence.
In a separate trial, an Ivory Coast national, Rudy Hermann Guede, was convicted of the murder.
