Experts in a Perugia courtroom said the DNA evidence linking her to the knife allegedly used to kill British student Meredith Kercher was unsound, Italian news agency ANSA reported Wednesday.
"The assertions are not sustainable," said a report by forensic specialists about alleged DNA from Kercher on a knife recovered in the home of Knox's ex-boyfriend Rafaele Sollecito.
Knox and Sollecito are appealing their sentences for the murder of Knox's former roommate Kercher, who was found with her throat cut in November 2007.
"There is no conclusive scientific evidence regarding the nature of the blood," the report said, also citing "erroneous findings" in earlier reports that traced DNA on the victim's bra strap to Sollecito.
Defense lawyers have claimed the DNA evidence was contaminated during the investigation and successfully petitioned for it to be re-examined in their appeal, ANSA said.
"We are thrilled," Knox's mother, Edda Mellas, told ABC News from Italy. "This is what our experts said all along. This is great news. We've always known Amanda is innocent."
Lawyer Luciano Ghirga was set to visit Knox in prison to explain the ruling to her, Mellas said.
The court is scheduled to consider the 144-page report filed Wednesday on July 25.