The prosecutor arguing U.S. student Amanda Knox's guilt in the 2007 murder of her British roommate says a DNA sample on the blade of the presumed murder weapon was clean and corresponds to the victim.

Prosecutor Alessandro Crini, in his second day of closing Tuesday, sought to dismantle genetic evidence cited by a Perugia appeals court when it overturned the guilty verdicts against Knox and co-defendant Raffaele Sollecito.

At the appeals level, the genetic trace attributed to Kercher in the first trial was deemed by new experts to be unreliable.

But Crini said the trace "has a clean genetic profile" and corresponds to the victim, Meredith Kercher.

Italy's highest court annulled the acquittals and ordered a second appeals court to re-evaluate the evidence, blasting the appellate ruling.