Updated 9.41am

ITALY’S HIGHEST COURT of appeal has overturned the acquittal of US student Amanda Knox 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.

The judges were expected to rule on Monday, but unexpectedly sought more time for deliberations, pushing the decision back to Tuesday.

The postponement of the ruling until this morning had sparked unease among lawyers representing the former lovers at the Rome court. Sollecito’s lawyer Giulia Bongiorno said beforehand that the delay was “rare… and hard to interpret.”

Prosecutors addressing the court on Monday said they were convinced the former lovers were guilty of murdering Kercher. They called for the judges to “make sure the final curtain does not drop on this shocking and dire crime.”

The defence argued that errors in DNA evidence had seen Knox and Sollecito wrongly accused from the start and called for their acquittal to be upheld.

Knox and Sollecito could face a re-trial in Florence, though Knox will likely 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.

Carloa Dalla Vedova, the lawyer of Amanda Knox, talks to reporters in front of Italy’s Court of Cassation in Rome yesterday (AP Photo/Riccardo De Luca)

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 has always denied the murder, is the only person still in prison for the crime.

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.

But the appeals judge quashed the convictions of Knox and Sollecito in 2011, largely over the admissibility of DNA evidence. The judges said the murder remained “unsolved” because it must have been carried out by more than one person.

Kercher’s family insists that 47 knife wounds on Meredith and the apparent use of two different knives in the attack meant that more than one killer was involved – which means that the second murderer is still at large.

In her first interrogation following the murder, Knox said – without a lawyer or an interpreter present – 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 that she was with Sollecito at his house all night and blamed her initial comments on exhaustion and police coercion.

The supreme court is also set to rule today on Knox’s appeal against a slander conviction for having blamed the bar owner, who was held in a cell for two weeks based on her allegations.

- © AFP, 2013

Read: Father of Meredith Kercher tells of moment he learned of daughter’s death >

Read: Kercher family ‘back to square one’ as Knox and Sollecito go free >