Earlier this year, Italy's highest court overturned their acquittals and ordered another trial.
Knox, now a 26-year-old University of Washington student in Seattle, has not returned to Italy for the trial, nor is she compelled by law to be there. The appellate court hearing the new case could declare her in contempt of court, but that carries no additional penalties.
"Facts are facts, and I'm not afraid of them," Knox told ABC News, but she will remain in the U.S. for the proceedings.
In 2009, Knox and , now 29, were found guilty of the murder of her 21-year-old roommate. They were sentenced to more than 20 years in prison by a court in , Italy. The couple was acquitted on appeal in 2011.
Knox, who spent four years in a Perugia prison, insists she's innocent. She says her presence at the retrial would only cause a repeat of the media circus of her first two trials, something she wants to avoid.
"'We refute the idea that because Amanda is not coming that Amanda is guilty, that Amanda is using a strategy. Amanda always said she was a friend of Meredith's, Amanda has always respected the Italian justice system," Knox's defence lawyer Luciano Ghirga told reporters before the trial opened.
Sollecito, an Italian who has been living in the Caribbean, says he will attend.
If Knox is found guilty, Italy could try to extradite her from the U.S. to serve a jail term.
Perugia bar owner Patrick Lumumba showed up at the trial Monday, saying he did so to underline the damage he suffered from Knox's false accusations. Three of the years Knox served in prison were for a slander conviction, for falsely accusing Lumumba in the murder.
Kercher's body was found in November 2007 in her bedroom of the house she shared with Knox in Perugia, a central Italian town popular with foreign exchange students. Her throat had been slashed.
A third man, Rudy Guede, was convicted in the slaying and is serving a 16-year term.