Italy's highest criminal court on Tuesday overturned Amanda Knox's acquittal in the slaying of her British roommate and ordered a new trial.
Knox called the decision "painful" but said she was confident in the truth.
The Court of Cassation ruled that an appeals court in Florence must re-hear the case against the American student and her Italian ex-boyfriend for the murder of 21-year-old Meredith Kercher. The exact issues that have to be reconsidered won't be known until the court releases its full ruling within 90 days.
Knox, now a student at the University of Washington, stayed up until 2 a.m. Seattle time to hear her fate and issued a statement through a family spokesman.
"It was painful to receive the news that the Italian Supreme Court decided to send my case back for revision when the prosecution's theory of my involvement in Meredith's murder has been repeatedly revealed to be completely unfounded and unfair," the statement said.
Knox said the matter must now be examined by "an objective investigation and a capable prosecution."
"No matter what happens, my family and I will face this continuing legal battle as we always have, confident in the truth and with our heads held high in the face of wrongful accusations and unreasonable adversity," Knox said in the statement.
Kercher's body was found in November 2007 in her bedroom of the house she shared with Knox and others in Perugia, an Italian university town where the two women were exchange students. Her throat had been slashed.
Prosecutors alleged Kercher was the victim of a drug-fueled sex game gone awry. Knox and Sollecito denied wrongdoing and said they weren't even in the apartment that night, although they acknowledged they had smoked marijuana and their memories were clouded.
An Ivory Coast man, Rudy Guede, was convicted of the slaying in a separate proceeding and is serving a 16-year sentence. Knox and Sollecito were also initially convicted of the murder and given long prison sentences, but were then acquitted on appeal and released in 2011.
The high court's ruling Tuesday overturned the appeals court acquittals.
"She thought the nightmare was over," Knox attorney Carlo Dalla Vedova said after the decision was released.
Italian law cannot compel Knox to return from the U.S. for the new trial. The appellate court hearing the case could declare her in contempt of court but that carries no additional penalties.
Della Vedova said Knox wouldn't come to Italy "for the moment" but would follow the case from home. He said he didn't think the new appeals trial would begin before early 2014. Asked if she would come to Italy for the trial, he said: "I don't think so."
It is unclear what would happen if she was convicted in a new appeals trial.