The decision by the Court of Cassation adds a further twist to a long-running case whose initial handling was sharply criticised by independent forensic experts.
Prosecutors accused Amanda Knox and her ex-boyfriend Raffaele Sollecito of assaulting and killing Kercher in 2007.
They were initially found guilty and sentenced to 26 and 25 years in prison respectively.
In 2011, their convictions were overturned and they were released after serving four years.
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Marjorie and Micheal Cawdery, both 83, were found dead in their house in Portadown, Northern Ireland on Friday.
Ann Myatt, who is contesting Jo Cox's former seat, told a hustings: "We've not yet shot anybody so that's wonderful."
The 26-year-old said she was moving on to the "next big chapter" - which includes a new show about her venture into motherhood.