Experts highlight more than 50 errors in how DNA evidence was collected to convict Amanda Knox

PROSECUTORS at Amanda Knox's appeal battled it out yesterday, with independent forensic experts saying some of the DNA evidence used to convict the American of murdering her British roommate was unreliable and possibly contaminated.

Italian 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 errors, including the wearing of dirty gloves to collect evidence.

Knox was convicted of sexually assaulting and murdering Meredith Kercher in 2007 in the apartment the two shared in Perugia and sentenced to 26 years in prison.

Knox's co-defendant and former boyfriend, Raffaele Sollecito, an Italian, 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 yesterday centred on a kitchen knife the prosecutors believe is the murder weapon.

In the first trial, prosecutors maintained Knox's DNA had been found on the knife handle and Kercher's DNA was found on the blade. They also said Sollecito's DNA was found on the clasp of Kercher's bra.

But the independent experts told the appeal 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 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. But Comodi insisted that the genetic profile found on the blade should not be tossed out.

She argued that no amount of contamination could have led to Kercher's DNA on the blade. Kercher never went to Sollecito's house.

The appeals court allowed the police chief who conducted the original investigation, Patrizia Stefanoni, to take the stand, granting a prosecutors' request.

Forensic consultants for prosecution and defence, who watched proceedings, will also be heard.

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, the head of the Italian police forensic unit, rejected the accusations, which he said damaged the image of the police and undermined the vital work they did.