Watching from afar
If the court convicts her, Knox will be ordered to return to Italy. If she refuses, Italy could request her extradition from the United States. But it's not clear if American authorities would comply.
Knox has said she would be willing to take a lie detector test.
"I'd do anything to prove my innocence," she told CNN affiliate ITV earlier this month. "I don't think that is necessary. But like I said, I'm doing everything to prove my innocence. It's just very sad that's what it has come to."
Knox isn't the only person watching the retrial from afar.
Citing health reasons, Kercher's family said in a statement that they decided not to return to Italy for the beginning of the trial after speaking "at great length."
"It is an extremely stressful time for us all and we desperately want to find truth and justice for Meredith, who was so brutally and unnecessarily taken from us, and so we have decided to support each other in the UK and follow closely here," the statement said.
The family said they would remain in close contact with their lawyer, who was in the courtroom Monday.
"We trust that the evidence will be reviewed and any additional testing requested to be granted so that any unanswered questions can be clarified and the court can clearly decide the next steps in this tragic case," the statement said.