A forensic biologist told an Italian court today the DNA of Amanda Knox and her slain roommate was found on a knife that police believe is the murder weapon.
Patrizia Stefanoni also testified that several blood samples were found in which the DNA of Knox and her former roommate Meredith Kercher were mixed together.
Stefanoni's daylong testimony came as the prosecution neared the end of its case in a drawn-out trial that began in January.
Kercher, 21, was found stabbed to death on Nov. 2, 2007 in the apartment she shared with Knox and two Italian women. Knox, 21 and her former Italian boyfriend Raffaele Sollecito, 25, are charged with the sexual assault and murder of Kercher in what prosecutors believe was a drug-fueled sex game.
A third person, Rudy Guede, 22, has already been convicted of murder and sexual assault in the case and is serving a 30 year prison sentence.
Stefanoni testified today that Knox's DNA was found on the handle of the kitchen knife the prosecution believes is the murder weapon. This knife was found in Sollecito's house. She said Kerches's DNA was on the blade. Stefanoni said, however, that the DNA in these samples was not from blood.
Stefanoni also said that in about 20 out of over 100 hundred samples taken from the crime scene she found Knox's genetic profile, or DNA. This is not unusual since Knox lived in the cottage, but significantly, in a number of the samples Knox's DNA was mixed with Kercher's DNA.
Most of the mixed DNA from the two women was found in blood traces discovered in the bathroom. Stefanoni told the court that Knox's DNA was found mixed with Kercher's in a luminol-enhanced bare footprint in the hallway outside Kercher's room,and in a luminol-enhanced spot found in the room of housemate Filomena Romanelli.
When the murder was discovered, Romanelli's room appeared to have been broken into. Her window was shattered and a large rock was found on the floor. Nothing was stolen, however, and investigators accuse Knox and Sollecito of faking the break-in after murdering Kercher.
In the small bathroom that Knox and Kercher shared, investigators found numerous spots of blood, including on the sink, the toilet, the bidet, the rug, the light-switch and the door jamb. Three of these blood stains – one on the edge of the sink, the one on the drain of the bidet, and one on a Q-tip box - contained the mixed DNA of Kercher and Knox
The significance of the mixed DNA was not explained in court, but in past reports the prosecution has theorized that Knox used that bathroom to wash-up after the murder, and due to a nose-bleed or some other injury, her blood mixed with that of the victim.
Knox's defense, however, has mentioned the possibility that it could be menstrual blood or blood from Knox's ear, which she had recently pierced. Knox had taken a shower in that bathroom the morning after the murder, before Kercher's murder had been discovered.
The DNA of Sollecito was found only in two samples out of the many taken in the house, one on a cigarette butt in the kitchen, and on the hook of Kercher's bra, mixed with Kercher's DNA.
Heated Cross Examination in Amanda Knox Trial
Kercher's bra was found on the floor in her room, soaked in blood and with the shoulder straps torn. The part of the bra with the hooks had been cut off. This fragment of the bra was taken into evidence a month after the crime when the forensic police returned to look for it and other items they had not taken the first time.
In the meantime, the crime scened had been searched and the house turned up-side down. Sollecito's defense maintains that the late collection of the piece of bra and the earlier search of the house has contaminated that particular piece of evidence.
Under a sometimes-heated cross interrogation by the defense lawyers for both Knox and Sollecito, Stefanoni defended her methods and denied the crime scene had been contaminated.
Sollecito would have had to rub the bra hook forcefully for DNA from his skin cells to be on it, she said. Dead skin cells floating around the room do not contain DNA and would not stick, she said.
Both defendants, who have been present in court for every hearing, followed the long and often highly technical explanations attentively. Although Knox has a court-appointed interpreter she no longer relies on her, but is able to follow the proceedings in Italian without help.
Knox's step-father, Chris Mellas, was present in court today, though he does not speak Italian and does not have an interpreter. At the end of Stefanoni's presentation, before her cross-interrogation, Knox turned to Mellas with a doubtful expression, but was otherwise relaxed and sunny.
Speaking to reporters at the end of the day's hearing, Mellas said Knox had told him she thought the day had gone very well. "We aren't worried about the DNA evidence presented today," Mellas said. "It is natural for Amanda's DNA to be in the house, she lived there."
Knox's parents, from Seattle, Wash., have defended their daughter and supported her from the start, taking turns staying in Perugia so there is always someone to visit her in jail the two times a week this is allowed. They are also allowed to call her once a week.
The trial continues on Saturday with more cross-questioning of Stefanoni and another witness for the prosecution, which should wrap up its witnesses next week.