(AP) -- An appeals court in Florence on Thursday upheld the guilty verdict against U.S. student Amanda Knox and her ex-boyfriend for the 2007 murder of her British roommate. Knox was sentenced to 28 1/2 years in prison, raising the specter of a long legal battle over her extradition if the conviction is upheld.

Lawyers for Knox and her co-defendant Raphael Sollecito vowed to appeal to Italy's highest court, a process that will take at least another year, dragging out a legal saga that has divided court-watchers in three nations.

In a statement from Seattle, where she had awaited the verdict, Knox said she was "frightened and saddened" by the decision, which she said was unjust and the result of an overzealous prosecution and narrow-minded investigation.

"This has gotten out of hand," she said. "Having been found innocent before, I expected better from the Italian justice system."

After nearly 12 hours of deliberations, the court reinstated the guilty verdicts first handed down against Knox and Sollecito in 2009 for the death of Meredith Kercher. Those verdicts had been overturned in 2011 and the pair freed from prison, but Italy's supreme court vacated that decision and sent the case back for a third trial in Florence.

Knox's attorney, Carlo Dalla Vedova, said he had called Knox by telephone and informed her that the Florence court had not only confirmed the guilty verdict, but had increased the sentence from the original 26 years.

"She was petrified. Silent," he said.

Sollecito was in court Thursday morning, but he didn't return for the verdict.

Sollecito's lawyers said they were stunned by the conviction and Sollecito's 25-year sentence and would appeal.

"There isn't a shred of proof," attorney Luca Maori said.

Presiding Judge Alessando Nencini ordered Sollecito's passport revoked but made no requests for Knox's movements to be limited, saying she was "justifiably abroad."

Experts have said it's unlikely that Italy would request Knox's extradition before the verdict is final. If the conviction is upheld on a final appeal, a lengthy extradition process would likely ensue.

Knox's defense team gave its last round of rebuttals earlier Thursday, ending four months of arguments in the third trial for Kercher's murder in the Italian university town of Perugia.

Kercher's brother and sister were in the courtroom for the verdict, and said the outcome was the best they could have hoped for.

"It's hard to feel anything at the moment because we know it will go to a further appeal," said her brother, Lyle Kercher. Asked if he was satisfied, he said: "No matter what the verdict was, it never was going to be a case of celebrating anything."

Knox's lawyer, Dalla Vedova, had told the court he was "serene" about the verdict because he believes the only conclusion from the files is "the innocence of Amanda Knox."

"It is not possible to convict a person because it is probable that she is guilty," Dalla Vedova said. "The penal code does not foresee probability. It foresees certainty."

Dalla Vedova evoked Dante, noting that the Florentine writer reserved the lower circle of hell for those who betrayed trust, as he asserted that police had done to Knox when they held her overnight for questioning without legal representation and without advising her that she was a suspect.

Knox had returned to Seattle after spending four years in jail before being acquitted in 2011. In an email to this court, Knox wrote that she feared a wrongful conviction.