ROME - An Italian news agency says Italy's top criminal court has ordered an American suspect in the slaying of a British student in Perugia and her two fellow suspects to remain in jail.

The Court of Cassation in its ruling Tuesday rejected a request by defense lawyers for the release of American university student Amanda Knox, 20, a University of Washington student from Seattle; her Italian ex-boyfriend, Raffaele Sollecito, 24, and an Ivory Coast citizen, Rudy Hermann Guede, 21.

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Amanda Knox, the 20-year-old UW student from Seattle, is pictured with her former boyfriend, Raffaele Sollecito, 24.

They are being held in the death of Meredith Kercher, 21, a student from Leeds University in England who was enrolled for a year of study in Perugia, about 110 miles north of Rome.

Kercher was found dead of a stab wound to the neck on Nov. 2, half-naked in a pool of blood in the apartment she shared with Knox.

Prosecutors have said she was killed resisting sexual assault, and the three in custody are under investigation for murder and sexual violence.

Knox and Sollecito have been jailed since Nov. 6. Guede was arrested in Germany, where he is believed to have fled shortly after the slaying.

All three deny wrongdoing, and no charges have been filed.

The high court will not examine evidence but focus on whether proper procedures were followed in the investigation, defense lawyers said.

"The Cassation will not rule on who is innocent or guilty," Knox lawyer Luciano Ghirga told reporters after making his case to the judges. "We have reiterated that some formal procedures were not valid."

Ghirga did not elaborate, but Knox's defense has complained that a lawyer was not present in an early questioning session. Prosecutors have countered that a lawyer was not needed because Knox was not a suspect at the time.

A prosecutor urged the judges to reject the defense's appeal, lawyers said during a break in the proceedings.

Judges in Perugia previously rejected defense requests to release the three and ruled that they could be held for up to a year as the investigation continued.