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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The Duke of Cambridge followed in his mother's footsteps today as he visited Commonwealth War Graves in Japan.
Arsenal legend Thierry Henry says it would be a dream to manage the club one day, but admits he's got to learn his trade first.
Across most of England and Wales it will be a clear, chilly night and Friday morning will start off cold but bright until cloud builds up.