The stabbing of 21-year-old Meredith Kercher, alleged sex games and multiple trials provided fodder for tabloids on both sides of the Atlantic and inspired books and films.

Knox said: "I just wanted to say that I'm incredibly grateful for the justice I've received, for the support that I've had from everyone, from my family to my friends to strangers to people like you... you saved my life and I'm so grateful, and I'm so grateful to have my life back. Thank you. That's all I can say.

"Right now I'm still absorbing what all of this means and what comes to mind is my gratitude for the life that's been given to me."

An emotional Knox added: "Meredith was my friend and it's ... she deserved so much in this life. I'm the lucky one."

The Court of Cassation threw out the second guilty verdict against Knox and her Italian former boyfriend Raffaele Sollecito, 31, for the murder, saying there was insufficient evidence to convict either of them.

Kercher, who was born in South London, was found stabbed to death in a house she shared with Knox in the medieval hill town of Perugia in 2007. Rudy Guede, originally from Ivory Coast, is serving a 16-year sentence for the crime, but judges in the previous trials ruled he did not act alone.

It had been widely expected that, even if the court overturned the previous convictions, it would order a retrial. Instead, both Knox and Sollecito are now definitively cleared.

Knox and Sollecito, who faced some 28 years and 24 years in jail, respectively, have both already served four years in jail after an original conviction in 2009.

The roundabout acquittals almost eight years after the murder are sure to stoke further controversy and questions about the Italian justice system, which has now twice overturned guilty verdicts in the case.