BRITISH student Meredith Kercher was stabbed by both Amanda Knox and Raffaele Sollecito, Italian judges said, as they explained what led them to issue guilty rulings in the 2007 murder case.
US student Knox and her former Italian boyfriend Sollecito were handed jail terms of 28 and a half years and 25 years, respectively, in January, after the case had been reopened following previous innocent verdicts.
In Italy it us customary for judges to file written explanations months after their rulings.
Kercher was stabbed in the neck by "two different knives" - a longer one wielded by Knox, a smaller one by Sollecito - judges from the Florence Court of Appeal wrote.
It was Knox who dealt the fatal blow, they added.
The court said on Tuesday Knox, Sollecito and Rudy Guede, an Ivory Coast-born small-time drug dealer who was tried separately and handed a final guilty ruling carrying a 16-year jail term, had jointly taken part in the murder.
They suggested that Kercher was killed following an argument between her and Knox which got out of hand, and also led to Guede sexually assaulting the victim and keeping her immobilised while the others stabbed her.
Judges said "it was not at all credible" to presume that Kercher was murdered because she backed out of taking part in a group sex game, as had been suggested in a first instance ruling on the case, in 2009.
"This reconstruction does not fit with the personality of the English girl," judges wrote.
Kercher shared a flat with Knox in Perugia, a central Italian town with a university for foreign students.
She was found on November 2, 2007, half-naked and with multiple stab wounds, inside her locked bedroom.
The court said Knox and Meredith "did not like each other", and suggested that, on the night she died, the victim confronted her US flatmate about the "uncivilised conduct" of Guede, who had been let into the house by Knox.
Police found Guede's unflushed faeces in a toilet.
Knox and Sollecito have always professed their innocence.
In a long legal saga, they were: arrested days after the crime, as prime suspects; convicted in 2009; acquitted and freed two years later; put on trial again in September, after a top court found procedural faults in their acquittal; and convicted again in January.
That judgment is not final, as it can be challenged again before Italy's top appeals body, the Court of Cassation.
But Knox has since returned to the US and indicated she would battle any extradition request.
Sollecito had his travel documents confiscated to prevent him from also fleeing abroad.
However, he is still free as, in Italy, jail sentences are normally not put into effect until all appeals procedures are exhausted.
