Italy's highest court of appeal overturned the acquittal of US student Amanda Knox on Tuesday and ordered a retrial over the murder of her British housemate in what prosecutors said was a drug-fuelled sex attack.
Knox and her Italian former boyfriend Raffaele Sollecito -- originally sentenced to 26 and 25 years in prison for killing and sexually assaulting Meredith Kercher in 2007 -- were acquitted on appeal in 2011 after four years in prison.
Both now face a retrial in a Florence court after judges upheld a 2012 prosecution appeal against their acquittals.
"It's not been easy from the start. We have had to climb a mountain, but we draw great strength both from being innocent and from the fact the court's ruling today is not a guilty verdict," Sollecito's lawyer Giulia Bongiorno said.
"The retrial means the court has decided some details need to be reviewed. The battle continues," she said.
Prosecutors addressing the court on Monday had said they were convinced the former lovers were guilty of murdering Kercher.
Calling for the judges to "make sure the final curtain does not drop on this shocking and dire crime," they said the acquittal, which was based mainly on the admissibility of DNA evidence in the case, contained "omissions and many mistakes".
Prosecutor general Luigi Riello had described it as "a rare mix of violation of the law and illogicality and should be overturned," and accused the appeal judge of having "lost of way".
Kercher, 21, was found half-naked with her throat slashed in a pool of blood in her bedroom in the house that she shared with Knox in November 2007.
A third person, Ivory Coast-born drifter Rudy Guede, who like the other two accused has always denied the murder, is the only person still in prison for the crime.
Kercher family lawyer Francesco Maresca punched the air in victory as the court's decision was read out,
according to journalists present.
"This decision serves to review the definitive and final truth of Meredith's murder. Guede was not alone, the judges will tell us who was there with him," he said.
The family has long claimed that Knox and Sollecito's acquittals left too many questions unanswered.
They -- and investigators -- insist that 47 knife wounds on Meredith and the apparent use of two different knives in the attack meant that more than one killer had been involved.
Knox is likely to be tried in absentia. The Seattle student returned home immediately after her release and the United States does not normally extradite its citizens to face legal action.
Prosecutors had alleged that Kercher was killed in a drug-fuelled sex attack involving Knox, Sollecito and Guede. They had said that it was the American student who delivered the final blows while the other two held the victim down.
The key to the appeal was an independent analysis of two pieces of evidence that had helped convict Knox and Sollecito -- a kitchen knife and Kercher's bra clasp.
The appeals judge quashed the convictions of Knox and Sollecito in 2011 largely over the admissibility of DNA evidence.
The review cast serious doubt on the original analysis, with experts and video evidence pointing to sloppy practice among the police at the crime scene and possible contamination of the evidence.
Knox has been repeatedly painted by her accusers as a seductive "she-devil" who had an unhealthy obsession with sex, while her defence has insisted she is simply a naive girl-next-door, a yoga lover whose nickname "Foxy Knoxy" referred to her childhood football skills.
In her first interrogation following the murder, Knox -- without a lawyer or an interpreter present -- said that she was in the house at the time, and falsely identified the owner of a bar where she worked as a waitress as the killer.
She later said she was with Sollecito at his house all night and blamed her initial comments on exhaustion and police coercion.
Sollecito also changed his story under questioning, but both students later blamed exhaustion and police coercion for their contradictory statements, which were made without lawyers present.