A pair of forensic experts testifying in Amanda Knox's murder appeal said Monday the police made a series of errors in collecting the DNA used to convict the American student of the 2007 killing of her roommate in Perugia, Italy.

Knox and her Italian ex-boyfriend, Raffaele Sollecito, were convicted of the murder of Meredith Kercher, a British student who shared an apartment with Knox while they were exchange students. Knox and Sollecito were sentenced to 26 and 25 years in prison, but both have consistently maintained their innocence.

In testimony Monday, the two experts appointed by the appeals court said the collection of the evidence did not meet international standards. Video footage from the crime scene showed a key piece of evidence, Kercher's bra clasp, being collected with a dirty glove. The experts said the clasp was not collected until weeks after the murder, making it contaminated evidence.

Prosecutors have maintained they found Sollecito's DNA on the clasp. The prosecution also said Knox DNA was on the handle of the knife used in the murder, while Kercher's was found on the blade. But the experts said they found no trace of Kercher's blood on the blade and that other DNA present on the knife was questionable.

The experts will be cross-examined by the prosecution when the appeal hearing continues Saturday.