Amanda Knox, the American student accused of murdering her British roommate Meredith Kercher in Italy, suffered a setback Friday after a judge ruled that her confession to being at the scene of the crime could stand as evidence.

Lawyers for Knox tried to get her written statement declared inadmissible but the judge said that it had been made voluntarily and not under duress.

As the court in Perugia prepared to hear evidence from the first witnesses — including officers from the Italian postal police who found Kercher's body — one of her lawyers said the defense objected to any use of the statement she made late at night on Nov. 6, 2007.

Carlo dalla Vedova said the statement, four days after the murder, had been made with no lawyer or interpreter present and was therefore invalid. In it, she admitted having been at the cottage the night Kercher was killed, saying she had covered her ears so as not to hear her roommate's screams. She also accused Patrick Diya Lumumba, a Congolese bar owner in Perugia, of being the murderer.

The "confession" has already been ruled as inadmissible by Italy's Supreme Court. However, it forms part of the case brought by Lumumba for damages after Knox withdrew her allegation, and is therefore included in the trial documents available to the judge and the six jurors, or "people's judges."

Knox, who appeared relaxed as she entered the courtroom wearing a green jumper and jeans, is standing trial jointly with her Italian ex-boyfriend Raffaele Sollecito. She smiled at Curt Knox, her father, who sat several rows behind in the vaulted and frescoed courtroom.

Sollecito got up and addressed the court Friday, saying he is the victim of a judicial error.

"It all seems unreal, I've got nothing to do with it," Sollecito said. "I'm not a violent person and the thought of hurting somebody has never crossed my mind … I feel I am the victim of a judicial mistake."

Kercher, a Leeds University exchange student from Surrey, England, was found dead in her bedroom, semi-naked and with her throat slashed. The prosecution maintains that she was sexually assaulted and then killed by Knox, Sollecito and Rudy Guede, an Ivory Coast immigrant brought up in Perugia, who has already been sentenced to thirty years in prison under fast-track procedures. The prosecution says the attack took place as part of a drug-fuelled "sex-game."

Click here to read more on this story from the Times of London.

The Associated Press contributed to this report.