Italy’s highest court, the Court of Cassation, has ruled that there must be a retrial of the case against Amanda Knox and her boyfriend Raffaele Sollecito for the sexual assault and murder of the British student Meredith Kercher in 2007.

At the time of the murder Kercher and the American Knox were flatmates in Perugia where they were both studying as exchange students.

Knox and Sollecito, her Italian boyfriend at the time, were originally found guilty in 2009 of the crimes and sentenced to 26 and 25 years respectively. They were then acquitted in a retrial in 2011 on the grounds that the DNA evidence produced at the first trial was flawed.

Prosecution lawyers subsequently appealed to the Court of Cassation to overturn the 2011 verdict on procedural grounds. The reasons why the court has granted the prosecution’s case are not yet known.

The Court of Cassation has also confirmed the three-year sentence given to Knox for the libel of Patrick Lamumba, a local Perugia bar owner, whom she originally accused of committing the Kercher murder.

The retrial of Knox and Sollecito, who became celebrities during their murder trials in Perugia, is expected to be in Florence.

Knox will probably be tried in absentia. If convicted it seems unlikely that the United States would agree to her extradition from Seattle where she is now living.

Rudy Guede, from the Ivory Coast, who was convicted of the Kercher assault and murder in a separate trial is serving a 16-year prison sentence.