Amanda Knox and her ex-boyfriend Raffaele Sollecito have been ordered to face trail again for the murder of British student Meredith Kercher.
"Whilst 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," said Stephanie Kercher, Meredith's sister.
Italy's Supreme Court overruled their acquittal on Monday after a six-hour hearing during which prosecutors and defence lawyers representing debated key evidence.
The pair will be tried again in Florence possibly by the end of this year or in 2014.
"I am really happy," said Francesco Maresca, a lawyer representing Meredith's family. "I had faith in the Supreme Court which is known for its preparation and crystal clear judgements."
Amanda, who now lives in Seattle, is not required to attend the retrial and is not expected to be extradited. "Amanda is very sad at this news but is strong and ready to fight on," said Amanda's lawyer Carlo dalla Vedova.
Amanda, 25, and Raffaele, who turns 29 on Tuesday, spent four years in jail but were freed on appeal in 2011 after an 11-month trial due to flawed DNA evidence and a lack of sound facts.
"We are hopeful," said Raffaele's lawyer Giulia Buongiorno. "We know Raffaele Sollecito is absolutely innocent."
Amanda and Raffaele were originally sentenced to 26 and 25 years respectively in a prison near Perugia in 2009 for murdering and sexually assaulting 21-year-old Leeds university exchange student Meredith. She was found dead in November 2007 in the house she shared with Amanda in Perugia. Prosecutors believed she was killed in a brutal sex game that went wrong.
In October 2008, Rudy Guede, from the Ivory Coast, was found guilty of sexually assaulting and murdering Kercher, and is serving 16 years in prison. He admitted being at the house on the night of the killing in November 2007 but denies murder.