Amanda Knox stayed in the United States as lawyers geared up for the retrial in Florence, Italy, for the 2007 death of Knox's British roommate Meredith Kercher.
The second trial of Knox and Raffaele Sollecito, her boyfriend at the time, was to begin Monday and both of the defendants said they would not attend, CNN reported.
Knox has maintained her innocence and has said she'd be willing to take a polygraph.
Knox and Sollecito were convicted in 2009 of murdering Kercher, a 21-year old British exchange student found stabbed to death in November 2007 in the house the two women were renting while attending classes in the Italian university town of Perugia.
The convictions of Knox and Sollecito were overturned in 2011 and Knox returned to her hometown of Seattle.
Italy's Supreme Court decided last year to return the case to the appeals court for retrial, saying the jury that acquitted Knox didn't consider all the evidence, CNN said.
The court's decision to retry the case "may be interpreted by the American authorities as double jeopardy -- twice tried for the same fact or the same case," Riccardo Montana, a law lecturer at City University in London, told CNN. "In Italy it's not like this, because this is still the same trial."
If she is convicted, Knox will be ordered to return to Italy. If she refuses, Italy could file an extradition request from the United State, CNN said, but it wasn't clear if U.S. officials would comply
Original headline: Amanda Knox retrial in death of Meredith Kercher to begin in Italy
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