An Italian court has ruled admissible a confession Amanda Fox had reportedly made after the death of British student Meredith Kercher.
In the note, it is believed she says that she had to cover her ears to block out Miss Kercher's screams as she was being stabbed to death in the white-washed cottage the two women shared in the Umbrian hilltop town of Perugia.
She is also thought to blame the killing on a Congolese bar owner, Patrick Diya Lumumba, who was later cleared of any involvement in the crime and has launched a civil action for damages against Miss Knox on the grounds that she defamed him.
It was written on November 6, 2007, four days after Miss Kercher's bloodied and half-naked body was found in her bedroom.
Miss Knox's lawyers argued that the hand-written document should not be accepted as evidence because it was written by the American student after she had spent most of the previous night being interrogated by Italian police.
But the presiding judge in the case, Giancarlo Massei, ruled Friday that the 'confession' can be used as evidence in the trial, which is expected to last months.
Miss Knox, 21, looked relaxed when she entered the medieval court room wearing a green sweater and jeans. It was a rather bad day for her. Apart from the judge's ruling on the confession, her former boyfriend and co-accused in the murder, Raffaele Sollecito, an Italian IT graduate, sought to distance himself from the crime that shook Europe.
The prosecution case is that Knox and Sollecito murdered the Leeds University student in the course of a group sex game that turned violent.
It is claimed that Sollecito and Knox acted with an Ivory Coast-born drifter, Rudy Guede, 22, to force Miss Kercher into the sex game. They then allegedly killed her when she resisted.
Guede, who came to Italy as a child from West Africa with his father, elected to undergo a separate trial last year and in October was convicted of murder by a judge. He was sentenced to 30 years in jail.
The trial of the other two has now begun in Perugia.
Mr Sollecito, 24, made a dramatic declaration of his innocence at the start of the proceedings.
His voice shaking, and pausing frequently to clear his throat, he told the court in Perugia that he "would not hurt a fly".
His emotional declaration was unexpected because the court had been scheduled to hear from the first witnesses in the case.
"As anyone who knows me will tell you, I would never hurt anyone, I would never hurt even a fly. I can't understand why I'm in this situation," Mr Sollecito told the court. "I have been in jail for 15 months and I don't have anything to do with this."
He pointedly omitted any protestation of innocence of behalf of his former girlfriend Miss Knox, who prosecutors say was responsible for stabbing Miss Kercher in the neck and causing her to bleed to death on the night of Nov 1, 2007.
He said he had started a "romantic relationship" with the University of Washington student on October 25th 2007, just a week before Miss Kercher's semi-naked body was found in the hillside cottage she shared with the American.
"There has been a lot of confusion in this case and I just want it all to be cleared up. "I ask you to investigate everything properly and thoroughly and not to have any presumptions because I feel that I am here as a result of a miscarriage of justice."
Mr Sollecito also told the court that he had never met Guede in his life, Nick Squires reported for Telegraph from Perugia.
The trial continues.