DNA Challenge Denied at Knox Murder Trial

Last Updated 9:35 a.m. ET

The trial of an American student for the slaying of her British roommate enters its most decisive stage this morning: the examination of DNA evidence that both the prosecution and defense holds as key to either conviction or acquittal.

The prosecution's case against Knox and her Italian former boyfriend Raffaele Sollecito is built largely on a sample of Knox's DNA found on a knife and Sollecito's on a bra belonging to the victim, British student Meredith Kercher.

But the bra sample came to light 47 days after the murder, reports CBS News correspondent Allen Pizzey, and the defense team is challenging the validity of the DNA evidence and the police handling of both samples.

On Monday Presiding Judge Giancarlo Massei rejected the defense's request to throw out the murder charges against Knox and Sollecito based on its challenges of the DNA evidence, and ruled that proceedings should go on. He argued that defense consultants were present when the DNA tests were carried out by forensic experts and said relevant documents had been made available a month and a half ago, suggesting that defense teams had enough time to review the DNA findings.

According to the prosecutors, Knox's DNA was found on the handle of a knife that might have been used in the slaying, while Kercher's DNA was found on the blade. The knife was found at Sollecito's apartment.

Knox's lawyer Carlo Dalla Vedova also argued Monday the DNA traces allegedly belonging to Kercher on the knife's blade were "too low" to be attributed with certainty.

Italian prosecutors say forensics and DNA experts have followed correct procedures while submitting the results of DNA tests to the court.

Knox and Sollecito, who were both in court as the trial resumed after a summer break, deny wrongdoing. Knox smiled to lawyers and family members as she walked in escorted by police guards.

Prosecutors allege that Kercher was killed during a sex game and that Knox fatally stabbed her in the throat.

A third person, Rudy Hermann Guede of the Ivory Coast, was convicted in a separate trial last year and sentenced to 30 years in prison. He denies wrongdoing and has appealed his conviction.

Knox's father is convinced the alledgedly-mishandled DNA samples will reinforce his daughter's alibi that she was with her boyfriend in his apartment when the murder was committed.

"Within the room in which Meredith lost her life . . . literally there's no speck of Amanda in that room - no fingerprint, no blood, no DNA anywhere," Curt Knox told CBS News.

Knox, who has been in jail almost 600 days already, told an acquaintance in court she was doing okay despite 90 degree temperatures in an un-air conditioned prison cell.

Pizzey reports that judgment is expected sometime in November, unless the DNA expert wants to reexamine all the evidence, which could add another 60 days onto the proceedings.