Italian prosecutors have appealed the decision to throw out Amanda Knox's murder conviction.
Knox was acquitted of British teenager Meredith Kercher's 2007 murder last October along with former-boyfriend Raffaele Sollecito, and freed from the Italian prison where she had been since her original trial in 2009.
The appeal is the final stage in the case against the pair, and had been widely expected.
A third defendant, Ivory Cost-born Rudy Guede, is currently serving a 16-year sentence for sexual assault and murder.
"We are petitioning against the decision of the Court of Appeals of Perugia and are optimistic it will be admitted to the Court of Cassation for review," said Francesco Maresca, the lawyer acting for the Kercher family, according to The Week.
The 112-page appeal filed by the Perugia prosecutors focuses on a controversial decision to review only two pieces of forensic evidence.
"We believe that either everything should be re-evaluated, or you say the court is able to judge for itself. This was a huge contradiction," said Maresca.
It is thought the court will decide on the appeal at the end of the year. No new evidence will be allowed to be submitted.
It was recently reported that Knox had sparked a "bidding war" among several top publishers for her memoirs.
The American has not spoken to reporters since her release, but for a short press conference immediately after arriving back in the United States.