THE sister of murdered British student Meredith Kercher has spoken of her family's ongoing ordeal after Italy's highest criminal court overturned Amanda Knox's acquittal for her killing.

The US student returned to her Seattle home when she was cleared after four years in jail in 2011.

She and co-accused Raffaele Sollecito face the prospect of an extradition request from the Italian government and a new trial in Florence.

Stephanie Kercher said it represented a step forward for the family who hope to discover what happened to the Leeds University student on the night she died.

She said: "There are a lot of unanswered questions. We are hopeful going back to court will help find those answers and find out the truth of what happened that night.

"While we are not happy about going back to court, and it will not bring her back, we have to make sure we have done all we can for her.

"We still have a long journey ahead and we are grateful for the support of the public. We just want justice for Mez."

The 21-year-old was found with her throat slashed in 2007 in her bedroom at the house she shared with Ms Knox in the Italian university town of Perugia.

Prosecutors claimed Ms Kercher, from Surrey, was the victim of a drug-fuelled sex game gone wrong.

Ms Knox, now 25, and her Italian ex-boyfriend Mr Sollecito, 29, denied wrongdoing.

They were convicted but later released by an appeal court.

Ms Knox, now a student at the University of Washington, said: "It was painful to receive the news. The prosecution's theory of my involvement in the murder has been repeatedly revealed to be unfounded and unfair.

"The prosecution responsible for the discrepancies in their work must be made to answer for them, for Raffaele's sake, my sake, and most especially for the sake of Meredith's family. Our hearts go out to them.

"No matter what happens, my family and I will face this con-tinuing 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."

Italian law cannot compel Ms Knox to return to the country for a fresh trial but she could face an extradition threat.

If any conviction was upheld at the country's highest court, and extradition was requested, it would be up to the US to decide if it would honour the request.

The US and Italy brought an extradition treaty into force in 1984. The treaty obligates each country to extradite anyone charged with or convicted of an extraditable offence, or any offences punishable under the laws of both countries by a jail sentence of more than one year.

The case mounted against them by prosecutors was ripped apart by the Italian appeals court, which noted the murder weapon was never found, DNA tests were faulty and prosecutors provided no motive for murder.

Italy's judicial system allows for two levels of appeals and enables prosecutors to contest acquittals.

The nature of the issues which led to the court order will only be disclosed when a ruling is released in the coming weeks.

Rudy Guede, a small-time drug dealer from the Ivory Coast, is the only person who remains behind bars over the case in Italy, where he is serving a 16-year sentence for sexually assaulting and killing the British student.