A witness called to the appeal trial in Italy of Amanda Knox accused the young American of murdering her British student roommate.

Rudy Herman Guede, who has already been convicted for his role in the killing, told the court Monday he believed that Knox and her boyfriend Raffaele Sollecito had stabbed Meredith Kercher.

Prosecutors have said Kercher was killed in the Perugia house she shared with Knox when a sex game turned violent on the night of November 1, 2007.

Knox said the was “shocked and anguished” by Guede's statement. Guede has admitted being at the house, but denies he was involved in the murder.

Knox was sentenced in December 2009 to 26 years in prison for the Kercher's murder. Sollecito, her boyfriend at the time, has been sentenced to 25 years.

Knox's mother, Edda Mellas said before entering the appeals trial that she hoped Guede's testimony would clear her daughter.

Guede's statement was in a letter read out to the court on Monday as he sat in the stand. The statement contradicted earlier testimony in which two convicted Italian criminals testified that Knox and her Italian boyfriend were innocent of the murder.

Mario Alessi, serving a sentence for kidnapping and killing a child, had told a court earlier that Guede had spoken to him about the murder when they shared a cell at Viterbo prison.

Guede has denied making any such statements.

Luciano Aviello, also in prison for his ties with organized crime, testified that his own brother killed the young British student during an attempted theft.