Video report by Paul Davies.
Italy's top court has ordered a retrial of American Amanda Knox and former boyfriend Raffaele Sollecito in the murder of British student Meredith Kercher, re-opening a case that prompted harsh criticism of the Italian justice system.
Kercher's half-naked body, with more than 40 wounds and a deep gash in the throat, was found in the apartment she shared with Knox in Perugia, where both were studying during a year abroad in 2007.
Prosecutors accused Knox and Italian Sollecito of killing the 21-year-old Leeds University student during a drug-fuelled sexual assault that got out of hand.
The two, who always professed their innocence, were initially found guilty in 2009 and sentenced to 26 and 25 years in prison respectively after a trial that grabbed headlines around the world.
In 2011, their convictions were quashed after forensic experts challenged evidence in the original trial, prompting accusations of a botched police investigation and leaving many aspects of the killing unexplained.
They were released after four years in prison and Knox returned to her family home near Seattle immediately afterwards.
On Tuesday, the Court of Cassation overturned the acquittal and accepted a request for a retrial from prosecutors and Kercher family lawyers who had criticized the earlier ruling as "contradictory and illogical".
The decision was immediately welcomed by the Kercher family lawyer Francesco Maresca who said it would provide an opportunity to find out what happened to Meredith.
"This is an important day for the Italian justice system," he said outside the court, criticizing the earlier judgment acquitting Knox and Sollecito as "extremely superficial".
"I've spoken to the family and Stephanie, her sister, is very happy, she's trying to understand what happens now."