The court heard six hours of arguments Monday and spent several hours deliberating that and a handful of other cases before announcing it would issue a decision at 10 a.m. (0900 GMT) Tuesday on whether the 2011 acquittals of Knox and her Italian ex-boyfriend Raffaele Sollecito will stand.
Italian prosecutors have asked the high court to throw out the acquittals of Knox and Sollecito in the murder of 21-year-old British student Meredith Kercher and order a new trial.
The high court normally issues the decisions the same day it hears arguments. But prosecutor general Luigi Riello told reporters that `'in very complex cases, it happens" that the court takes another day.
Lawyers for Sollecito declined to speculate on what the delay could mean for the decision. Sollecito's father was calm about the development.
`'We have waited so many years, one night is not going to make a difference," Francesco Sollecito said outside the courthouse. He said he hadn't spoken to his son, who did not attend the hearing, about the day's proceedings.
Knox, meanwhile, was waiting anxiously in Seattle to hear if her long legal battle is over.
"She's carefully paying attention to what will come out," attorney Luciano Ghirga said as he arrived at Italy's Court of Cassation in Rome. "This is a fundamental stage. The trial is very complex."
Knox, now 25, and Raffaele Sollecito, who turns 29 on Tuesday, were arrested in 2007, shortly after Kercher's body was found in a pool of blood in her bedroom in the rented apartment she shared with the American and others in the university town of Perugia, where they were exchange students. Her throat had been slashed.
Prosecutors alleged that Kercher was the victim of a drug-fueled sexual assault.
Knox and Sollecito have both maintained their innocence, although they said that smoking marijuana the night Kercher was killed had clouded their recollections.
Knox and Sollecito were convicted and given long prison sentences: 26 years for Knox, 25 for Sollecito. But an appeals court acquitted them in 2011, criticizing virtually the entire case mounted by prosecutors. The appellate court noted that the murder weapon was never found, said that DNA tests were faulty and added that Knox and Sollecito had no motive to kill Kercher.
After nearly four years behind bars in Italy, Knox returned to her hometown of Seattle and Sollecito resumed his computer science studies. Knox is now a student at the University of Washington, according to her family spokesman, Dave Marriott.
In the second and final level of appeal, prosecutors are now seeking to overturn the acquittals, while defense attorneys say they should stand.
The court can decide to confirm the acquittal, making it final, or throw out the Perugia appellate court ruling entirely or partially, remanding the case to a new appeals court trial.
In that case, Italian law cannot compel Knox to return to Italy. The Italian appellate court hearing the case could declare her in contempt of court but that carries no additional penalties.
It is unclear what would happen if she was convicted in a new appeals trial.
`'If the court orders another trial, if she is convicted at that trial and if the conviction is upheld by the highest court, then Italy could seek her extradition," Knox's lawyer Carlo Dalla Vedova said.
Italy is not obliged to seek her extradition but it could decide to do so. Then it would be up to the United States to decide if it honors the request. U.S. and Italian authorities could also come to a deal that would keep Knox in the United States.
Riello, the prosecutor general, argued before the court that there were ample reasons `'not to bring down the curtain on the case."
Riello said the appellate court was too dismissive in casting aside DNA evidence that led to the conviction in the lower court, arguing that another trial could make way for more definitive testing.
Defense attorneys said they were confident the acquittals would be upheld.
"We know Raffaele Sollecito is innocent," said his attorney, Giulia Bongiorno, who called the entire case "an absurd judicial process."
Before the court, Bongiorno argued there was an `'unending series of errors by scientific police" in how they handled evidence in the case, including the fact that the crime scene had been disturbed `'and possibly contaminated" during the investigation.
A young man from Ivory Coast, Rudy Guede, was convicted of the slaying in a separate proceeding and is serving a 16-year sentence. Kercher's family has resisted theories that Guede acted alone.
The lawyer for the Kercher family, Francesco Maresca, said the family was likely to issue a statement when the decision is announced. They did not attend the arguments.
The court is also hearing Knox's appeal against a slander conviction for having accused a local pub owner of carrying out the killing. The man was held for two weeks based on her allegations, but was then released for lack of evidence.
Riello argued that conviction should stand because `'you cannot drag in an innocent person while exercising your right to a defense."
Knox's lawyer Dalla Vedova said the slander verdict should be thrown out because Knox had not been advised that she was a suspect during the questioning.
`'The girl was confused, worn out" after 14 hours of questioning by police that stretched overnight, Dalla Vedova said, adding that while Knox was alone, 36 investigators signed the interrogation sheet.
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