"I am not in the courtroom because I'm afraid," Knox wrote in an email to the court from the United States, where she is a student, ANSA reported.
"I fear that the vehemence of the accusations will impress you, will pull the wool over your eyes and will blind you," she said.
A court in Florence court is trying the case against Knox and her ex-boyfriend, Raffaele Sollecito, who have denied killing Meredith Kercher in 2007 in Perugia in what prosecutors said was a sex game gone wrong.
Knox and Sollecito have spent four years in prison, including custody before their first trial in which they were convicted murder in 2009. An appeals court overturned those convictions in 2011 and Knox returned to the United States. However, Italy's top court ordered a new trial at the appeals court level over aspects of the evidence it said hadn't been properly examined previously.
In her email, which Judge Alessandro Nencini called "irregular," Knox called Meredith Kercher her friend, ANSA said.
"I didn't kill Meredith," said Knox, who is living in Seattle. "She was nice, she helped me, she was generous and funny."
An Italian prosecutor is seeking 26 years in prison for Knox and Sollecito for the murder, plus another four years for Knox for allegedly slandering a bar owner she implicated during a police interrogation while later retracting.
A decision is expected Jan. 10.