An Italian prosecutor has demanded that an appellate court find Amanda Knox guilty of the 2007 murder of her roommate.

Prosecutor Alessandro Crini said that the killing may have been sparked by arguments about cleanliness and triggered by a toilet left unflushed by the only man now in jail for the murder.

He demanded 26-year sentences for Ms Knox and Raffaele Sollecito, her co-defendant and former boyfriend, following more than 10 hours of closing arguments over two days.

Ms Knox and Ms Sollecito deny any involvement in the killing.

Mr Crini departed from past scenarios by suggesting the crime was not so much sexually fuelled but an act of physical violence with a sexual expression.

He alleged that Ms Knox and Mr Sollecito acted with another man in an explosion of violence sparked by tension between Ms Knox and British student Meredith Kercher.

Mr Crini argued that Rudy Guede -- a native of Ivory Coast now serving a 16-year sentence for the murder -- may have inflamed tensions between Ms Knox and Ms Kercher after he defecated in a toilet inside the women's apartment and didn't flush it.

Kercher's murder in the idyllic hillside town of Perugia is getting its third trial after Italy's highest court annulled an appellate ruling overturning the 2009 guilty verdicts against Knox and Sollecito. They were convicted in the first trial, and sentenced to 26 years and 25 years, respectively.

Ms Knox's lawyer, Carlo Dalla Vedova, said the shift in the prosecution's theory about events leading up to the killing "confirms the lack of proof".

The trial continues until December 16 with closing arguments by the Kercher family lawyer followed by Ms Knox's defence team the next day. A verdict could come in January.

Irish Independent