ROME (AP) — A police forensic expert testified Friday that a knife prosecutors say might have been used to slay a British student bore traces of the DNA of a U.S. co-defendant in the murder trial in Perugia, Italian news reports said. 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. Defense 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 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.? After Stefanoni testified, Knox?s lawyer told reporters outside the courtroom that he and that the defense was considering asking the court to order DNA testing by an outside expert. ?Nothing has changed. Our positions are in clear contrast when it comes to the scientific findings,? lawyer Luciano Ghirga said. Sollecito?s lawyer, Giulia Bongiorno, also challenged Stefanoni, reiterating defense contentions that the clasp was contaminated since it wasn?t collected by forensic experts until several weeks after the slaying. She also said it was found some distance away in the room them when it was first noticed under a pillow in the bedroom where Kercher?s body was found, with stab wounds to the neck. 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 slaying.