Meredith Kercher was killed in Perugia in 2007.
What was the motive for the killing?
Prosecutors said it was the result of a four-way sex game in which Miss Knox, Mr Sollecito and Rudy Guede, a small-time drug dealer from Perugia of Ivory Coast origin, forced Kercher to submit to sex, and then killed her with a knife or knives.
But Miss Knox knew Guede only casually, and Mr Sollecito did not know him at all. Only one person, an Albanian immigrant, claimed to have seen all three of them together, but his evidence was dismissed as unreliable early in the trial.
None of the accused had a history of violence or sexual assault. Defence lawyers ridiculed the idea that Miss Knox and her new boyfriend would have sought a dangerous sexual liaison given that they had only been going out together for a few days and appeared madly in love.