Amanda Knox
© The Associated Press/The Canadian Press/Elaine ThompsonIn this Oct. 4, 2011 file photo, Amanda Knox, standing in front of her father, Curt Knox, and other supporters, speaks at a news conference shortly after her arrival at Seattle-Tacoma
Italian prosecutors filed an appeal to the country's highest court on Tuesday seeking a new trial for Amanda Knox of Seattle and her onetime boyfriend, Raffaele Sollecito, in the fatal stabbing of a British student in Perugia, Italy.

The appeal was filed four months after an appellate court overturned the 2009 convictions of Ms. Knox and Mr. Sollecito, in the murder of Meredith Kercher, a British exchange student found dead in November 2007 in the apartment she shared with Ms. Knox.

The appeal had been expected as part of the appeals in the Italian justice system, which could stretch out for some time. If it is granted, prosecutors could retry Ms. Knox in absentia, if necessary, and she could ultimately face extradition if convicted. But her lawyers dismissed that outcome as highly unlikely.

"We're not considering that possibility; for us she has been acquitted," said one of her lawyers, Luciano Ghirga. "That's how the system works, but for us it's a hypothesis far into the future."

Carlo Dalla Vedova, who also represents Ms. Knox, denounced reviving the case, saying it would "reopen painful wounds" and again draw attention to a sensational tale of sex and violence. "I am sorry for the two kids," he said of Ms. Knox, 24, who moved back to her hometown, Seattle, after her release from prison, and Mr. Sollecito, 27, who has been living in southern Italy.

"But I am especially sorry for Meredith Kercher; silence would have been better," he said by telephone.

Speaking to reporters in Perugia on Tuesday, the prosecutors Giovanni Galati and Giancarlo Costagliola said they remained convinced that Ms. Knox and Mr. Sollecito were guilty of the killing, the news agency ANSA reported. And they challenged the October decision to overturn the conviction, arguing that it was "full of errors," ANSA reported.

In their original case against Ms. Knox and Mr. Sollecito, prosecutors suggested that the killing was the result of a drug-fueled game of rough sex gone awry, involving a reluctant victim, the two defendants and a third man, an Ivorian living in Perugia, Rudy Guede. The seminaked body of Ms. Kercher was found under a duvet, her throat slit, in the house the women shared.

After two appeals, Mr. Guede was found guilty in 2010 of participating in a homicide and is serving a 16-year sentence.

While the prosecutors won convictions of Ms. Knox and Mr. Sollecito in the original case, serious questions were raised about the prosecutor's theory of the crime and the quality of the evidence. After an independent review cast doubt on the DNA evidence, the appellate court ruled that the prosecution's case no longer stood up.

The Supreme Court will not hear new evidence, ruling only on the appeal presented by the prosecution and whether or not proper legal procedures have been followed, Mr. Dalla Vedova said.

Last week, Ms. Knox's defense also filed its appeal in the same case, asking the Supreme Court to overthrow her conviction on slander charges, which was upheld by the appellate court last October. Ms. Knox was found guilty of falsely accusing her former employer, the barman Patrick Lumumba, of being at her apartment on the night that Ms. Kercher was killed. He was arrested but later released. Ms. Knox later said she had been pressured to accuse him.

Mr. Ghirga said he thought the Supreme Court would rule on the admissibility of the appeal later this year.

On Tuesday lawyers for the Kercher family also challenged the appellate court's ruling, "in the interests of the family," said their lawyer, Francesco Maresca.

Ms. Knox is not required to attend the Supreme Court hearing. She could, however, return to Italy in June, Mr. Dalla Vedova said, as a witness in a trial involving her parents, who have been charged with defamation through the press after they said in an interview in a British newspaper that Ms. Knox had told them that she had been verbally and physically abused by the police.

Mr. Dalla Vedova said his client was not worried because her innocence had "been proven." He added, "We're just sorry she has to deal with all this again."