Amanda Knox claims there is "no logic" to an Italian court's decision to reinstate her conviction for the murder of British student Meredith Kercher.
The appeal court in Florence has issued a 337-page document explaining why it restored the guilty charge against Knox and her former Italian boyfriend Raffaele Sollecito in January.
It says it was American former student Knox who delivered the fatal knife blow to her 21-year-old roommate in 2007.
It adds that the British student's wounds indicate multiple aggressors and that the two exchange students fought over money on the night of her death.
Kercher and Sollecito were first convicted for the murder in 2009 but acquitted by the High Court in 2011 and released from prison. The appeal court convicted them for a second time in January.
In a written statement Knox said "I am innocent."
She said forensic evidence refutes the appeal court's theory that more than one person attacked Kercher and that a small kitchen knife was used in the murder, the Associated Press said.
Knox says she will now take the case to Italy's Supreme Court for an appeal.
If the court confirms the conviction a long extradition fight is expected for Knox, who is now living back in America.
Ms Kercher, 21, was found dead in the flat she and Knox shared in the town of Perugia. Her throat had been slashed and she had been sexually assaulted.
In its explanation the appeal court said that a third person convicted of the murder, Rudy Hermann Guede, did not act alone, and cited the nature of the victim's wounds, as well as finger imprints on her body indicating she had been restrained.
The said it had evidence of a fallout between the two roommates, including statements by Guede under police questioning that Ms Kercher had accused Knox of taking money from her room.
The document said : "It is a matter of fact that at a certain point in the evening events accelerated; the English girl was attacked by Amanda Marie Knox, by Raffaele Sollecito, who was backing up his girlfriend, and by Rudy Hermann Guede, and constrained within her own room."
It ruled out a sex game gone wrong because it was not in Ms Kercher's character.
Guede was convicted in a separate trial of sexually assaulting and stabbing Kercher. His 16-year sentence - reduced on appeal from 30 years - was upheld in 2010 by Italy's highest court, which said he had not acted alone.