Amanda Knox delivered the fatal blow to Coulsdon student Meredith Kercher, Italian judges have said.
Having reinstated the guilty verdict against Knox, the judges explained their ruling by saying it was she who "delivered the only mortal blow", striking Miss Kercher with a kitchen knife.
Judges said they believe Knox and her former boyfriend, Raffaele Sollecito, both carried knives while Rudy Guede held the victim down and sexually assaulted her.
Knox and Sollecito were originally convicted of the murder in 2007. They were acquitted on appeal in 2011, but the ruling was overturned in January.
Guede is currently serving a 16-year prison sentence after being convicted of Miss Kercher's murder at an earlier trial.
Knox's trial will go to Italy's highest court if she and Sollecito appeal the ruling.
At the moment, Knox is sentenced to 28 years and six months. while Sollecito has 25 years.
If the current verdict is upheld, officials will have to begin attempts to extradite Knox from the US, where she returned after being released from prison in 2011.
