Perugia prosecutors filed the 112-page appeal, more than four months after an appeals court threw out the convictions against Knox, 24, and Raffaele Sollecito, 27.
Prosecutors Giovanni Galati said he is "very convinced" that Sollecito and Knox were responsible for the Nov. 1, 2007, stabbing death of Meredith Kercher, a 21-year-old British student who shared an apartment with Knox in the university town of Perugia.
Galati told reporters in Pergugia that the appeals sentence must be thrown out, saying it was full of "ommissions and many errors," the news agency ANSA reported.
The prosecutors appeal, which was expected, marks the third and final stage in the criminal case against Knox and Sollecito.
A statement released by the Knox family spokesman Tuesday said the appeals trial clearly established Knox's innocence. It called the latest appeal "simply another example of harassment by the prosecution against Amanda."
Knox and Sollecito were found guilty in a lower court of slaying Kercher in what prosecutors described as a sex-fueled attack, and sentenced to 26 years and 25 years respectively. An appeals court then said the evidence did not hold up, freeing Knox to return home to the United States after serving four years in prison. Sollecito lives in Italy.
Luca Maori, Sollecito's lawyer, said the high court is expected to issue its decision toward the end of the year.
The prosecutors move was expected, and Maori said he would file his counter-arguments after going over the prosecutors' appeal.
"We will write our brief to say it's a mistake," Maori said.
The high court cannot hear new evidence, and will make its decision based on what has been submitted in earlier trials.
The fatal blow to the prosecution's case was a court-ordered DNA review in the appellate trial that discredited crucial genetic evidence used to convict Knox and Sollecito in 2009.
Kercher was found slain in a pool of blood in the house she shared with Knox in Perugia. The appeals court in October said the guilty verdicts against the pair were not corroborated by any evidence, and that the court hadn't proven they were in the house when Kercher was killed.
Still, the appellate panel stopped short of saying what might have happened the night of the murder.
A third defendant, Ivory Coast-born drifter Rudy Guede, was convicted in a separate trial of sexually assaulting and stabbing Kercher. His 16-year sentence, reduced in appeal from an initial 30 years, was upheld by Italy's highest court in 2010.
More Northwest Headlines
Court denies Medina millionaire’s release from Montana jail Wastewater levels in Spokane River high due to drought 11:10 a.m. Bystanders help but couldn’t save man who drowned in Kitsap County 11:09 a.m. Vancouver drama teacher pleads guilty to sex with student 11:08 a.m. Warm blob of ocean water, drought warming Puget Sound water 11:06 a.m. Public has until Aug. 28 to comment on Hanford plan 11:05 a.m. Yakima hospital to affiliate with Seattle’s Virginia Mason 11:02 a.m. Data shows few Latino voters in Yakima so far 11:01 a.m.
Our new comment system is not supported in IE 7. Please upgrade your browser here.