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.
More top news
Teenager Leah Washington had her leg amputated after being involved in a rollercoaster crash at Alton Towers.
The video, obtained by ITV News, shows scores of migrants desperately trying to board lorries in a restricted area within the tunnel.
Ex-Spitfire pilot Allan Scott, 94, said he was told off by the Queen when he first met her in 1943 when she was just 16.