Prosecutors at Amanda Knox’s appeals trial battled it out yesterday with independent forensic experts who say some of the key DNA evidence used to convict the American student of murdering her British roommate 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 co-defendant and 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 yesterday’s debate 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 last 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.