Prosecutors at Amanda Knox's appeal trial have battled it out with independent forensic experts who say some of the key DNA evidence used to convict the American student of murdering her British room-mate was unreliable and possibly contaminated.
Prosecutor Manuela Comodi sought to undermine the experts' conclusions and show that the forensic evidence used to convict Knox could stand.
The experts - who were appointed by the court to review the evidence and the procedures used to obtain it - maintain that the original investigation was marked by some glaring errors. They have mentioned more than 50, including the wearing of dirty gloves in collecting evidence.
Knox was convicted of sexually assaulting and murdering Meredith Kercher, from Coulsdon in Surrey, in 2007 at the apartment the two shared in Perugia and sentenced to 26 years in prison. Knox's ex-boyfriend, Raffaele Sollecito of Italy, was convicted of the same charges and sentenced to 25 years. Knox, 24, and Sollecito, 27, have denied wrongdoing and have appealed.
Much of the debate at the trial on Saturday centred on a kitchen knife prosecutors believe to be the murder weapon. In the first trial, prosecutors maintained that Knox's DNA was found on the knife's handle and Kercher's DNA was found on the blade. They also say Sollecito's DNA was found on the clasp of Kercher's bra.
But the independent experts told the appeals court earlier in the week that the collection of evidence fell below international standards. They said the knife was not properly sealed or kept after it was found at Sollecito's house, opening the way to possible contamination.
The experts said that the DNA on the blade could not be attributed with certainty to Miss Kercher. They reviewed the procedures used to test the original DNA material, concluding that the genetic quantity was below the minimum amount necessary for the test to be considered reliable.
"There is a complete genetic profile, but it's not reliable," testified Carla Vecchiotti, one of the court-appointed experts. "We don't know if Meredith's DNA was on it or not," Ms Vecchiotti said. Ms Vecchiotti and her partner in the review, Stefano Conti, are forensic experts from La Sapienza University in Rome.
Ms Comodi insisted that the genetic profile found on the blade should not be thrown out. She argued that no amount of contamination could have led to Miss Kercher's DNA being on the blade. Miss Kercher never went to Sollecito's house.
The appeals court on Saturday allowed the police chief who conducted the original investigation, Patrizia Stefanoni, to take the stand, granting a prosecutors' request. The experts' strong criticism of the investigation methods led to a letter of protest by forensic police, which was read in court by the presiding judge. Piero Angeloni, head of the Italian police forensic unit, rejected the accusations, which he said hurt the image of police and undermined their work.