MILAN >> The Italian appeals court that reinstated the conviction against Amanda Knox in her British roommate’s 2007 murder said in a lengthy reasoning made public Tuesday that Knox herself delivered the fatal blow out of a desire to “overpower and humiliate” the victim.

Presiding Judge Alessandro Nencini concluded in a 337-page document that the evidence “inevitably leads to the upholding of the criminal responsibility” against Knox and her former Italian boyfriend Raffaele Sollecito for the murder of 21-year-old Meredith Kercher in a hillside villa occupied by students in the university town of Perugia.

The judge said the nature of Kercher’s wounds, which he said were inflicted by two knives, and the absence of defensive wounds indicated multiple aggressors were to blame, also including Rudy Hermann Guede, an Ivorian man convicted separately and serving a 16-year sentence.

Nencini presided over the Florence-based panel that reinstated the first trial guilty verdicts against Knox and Sollecito in January, handing Knox a 28 1/2 year sentence including the additional conviction on a slander charge for wrongly accusing a Congolese bar owner. Sollecito faces 25 years.

The release of the court’s reasoning opens the verdict to an appeal back to the supreme Court of Cassation. If it confirms the convictions, a long extradition fight for Knox is expected.

The University of Washington student has been in the United States since 2011, when her earlier conviction was overturned. Knox, 26, has vowed to fight the reinstated conviction, saying she would “never go willingly” to Italy to face her judicial fate.

In a statement Tuesday, Knox said the reasoning “is not supported by any credible evidence or logic. There is simply no basis in the record or otherwise for this latest theory.” She said she remained “hopeful the Italian courts will once again recognize my innocence.”

Sollecito’s lawyer, Giulia Bongiorno, tore apart the reasoning, saying “from the motive, to weapon, to the DNA, it is a string of errors.”

At one point, Nencini wrote that Kercher and Sollecito’s DNA were found in a mixed trace on the kitchen knife alleged by prosecutors to have been the murder weapon. Bongiorno said that there was never any such finding.

The judge said relations between Knox and Kercher were strained, despite Knox’s attempts to downplay tensions during the trial, and that the two had argued over housekeeping and visitors.

He also cited as credible Guede’s statements that the British student had accused Knox that evening of stealing rent money from her room, even though none of the defendants was convicted of the theft. He noted that 300 euros (more than $400) had been withdrawn from her bank, but never accounted for. Whether or not the accusation was founded, Nencini said it indicated Kercher’s “negative view” of Knox.

Nencini’s reasoning assigned the role of each assailant: Sollecito, now 30, used a small knife that caused a wound to the right side of Kercher’s neck and also was used to remove her bra, the judge wrote, while Guede restrained and sexually assaulted the victim. Knox “delivered the only mortal blow,” striking Kercher with a kitchen knife causing an eight-centimeter (three-inch) wound, the judge wrote.

The three trials have only physically identified one murder weapon, a kitchen knife found in Sollecito’s drawer. Forensic tests attributed DNA on the handle to Knox and on the blade to Kercher, although that evidence was placed in doubt by new experts in the first appeal that acquitted the pair. No smaller, second knife has ever been entered into the evidence.

As for motive, the judge said that the aggression, exacerbated by Knox’s and Sollecito’s drug use, grew out of Kercher’s exasperation with Knox and was ignited by Kercher’s anger at Guede’s presence in the apartment and his “uncivilized” behavior by leaving a toilet unflushed.

While Guede was motivated by “sexual instinct,” Knox and Sollecito were motivated by “a desire to overpower and humiliate the British girl,” Neninci wrote.

He said the murder was not attributable to a sex game gone awry, as the first trial concluded, because it was out of Kercher’s character to have consented to such activity.

Kercher was found dead in a pool of blood in the apartment she and Knox shared in the town of Perugia, on Nov. 2, 2007. Her throat had been slashed and she had been sexually assaulted. Knox and Sollecito were arrested four days later and served four years in prison before an appeals court acquitted them in 2011. Knox returned to the Seattle, where she is a student at the University of Washington.

Italy’s high court later threw out that acquittal in a scathing decision and ordered a new trial, resulting in January’s conviction. Both Knox and Sollecito deny any involvement in Kercher’s death, and say they spent the evening at Sollecito’s place getting high, having sex and watching a movie.

The courts have cast wildly different versions of events. Knox and Sollecito were convicted of murder and sexual assault in the first trial based on DNA evidence, confused alibis and Knox’s false accusation against a Congolese bar owner, for which she was also convicted of slander.

Then an appeals court in Perugia dismantled the murder verdicts, criticizing the “building blocks” of the conviction, including DNA evidence deemed unreliable by new experts, and lack of motive.

That acquittal was vacated in March 2013 by Italy’s highest court, which ordered a new appeals trial to examine evidence and hear testimony it said had been improperly omitted by the Perugia appeals court, and to redress what it identified as lapses in logic.

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Paolo Santalucia in Rome contributed to this report.