Amanda Knox: innocent abroad, or a calculating killer? Now the jury must decide

The American student's murder trial begins today – and Italy is transfixed, reports Peter Popham

More than 140 reporters and cameramen are expected to squeeze into a court house in the city of Perugia this morning for the opening of what has been billed as Italy's trial of the year. And all eyes will be on Amanda Knox, the 21-year-old American student whose sexual appetites are at the centre of the case.

In the dock with her will be her24-year-old ex-boyfriend Raffaele Sollecito. They have spent more than a year in Perugia's jail waiting to be tried for their alleged role in the murder of the Surrey student Meredith Kercher, 21, sexually assaulted and stabbed to death in her Perugia bedsit in November 2007.

Ms Knox leapt to notoriety in the days after the murder, kissing and cuddling Mr Sollecito in front of the lenses of the cameras, and her wildly conflicting accounts of how she had passed the evening on which her flatmate Meredith died put her under investigation. Those accounts included a confession, later retracted, that she had heard Meredith's screams but had merely blocked her ears.

Despite being behind bars the whole time, the vivacious, sexually adventurous, guitar-playing student from Seattle has become a minor celebrity in Italy, ranked in a poll in December as one of Italy's "women of the year". Her Christmas activities in jail were minutely reported – nuns taught her how to dance and she watched Kung Fu Panda – as was her poignant plea to her family for thermal underwear, warm socks and flannel sheets. When she played a walk-on part in a video shot in the prison, in which she recited Hamlet's "To be or not to be" speech, the issue of whether or not the video should be screened at a film festival became a national controversy (in the end, it was not). Her diaries have been leaked to the press and are minutely scrutinised for evidence of sexual deviancy. It is all prurient and intrusive but by no means irrelevant. For the question of Ms Knox's sexual appetites, and how far she will go to gratify them, go to the heart of this disturbing case.

One person is already serving a long jail sentence for killing Ms Kercher: Rudy Guede, 22, originally from the Ivory Coast, was found guilty of murdering her after a fast-track trial that finished in October, and was sentenced to 30 years. But prosecutor Giuliano Mignini has maintained from the first weeks of the investigation that Ms Knox and Mr Sollecito were also involved, and the judge in Guede's trial, Paolo Micheli, not only endorsed that view but said that the "risk of their repeating the offence" was so strong that neither of the accused could be let out on bail, although both have clean records.

At the end of that first trial, Mr Mignini told Judge Micheli that Ms Kercher's murder "was premeditated ... a 'rite' celebrated on the occasion of the night of Halloween", postponed for one day because there was a Halloween dinner party in Ms Kercher's room. He added: "The presumed assassins contented themselves with the evening of 1 November to perform their do-it-yourself rite, when for some hours it would again be the night of All Saints." He described the murder scene, saying Ms Kercher was on her knees, Guede holding her rigid and Mr Sollecito grasping one arm while Ms Knox wielded the knife. The satanic Halloween rite version of the murder has gone around the world, but Judge Micheli rejected it out of hand in his summing-up. Mr Mignini's Halloween scenario was "to say the least, a fanciful descriptive reconstruction", he wrote, which belonged to the world of comic books. Nor did the judge give much credit "to the kneeling position espoused by the prosecutor in describing a scene suggestive of an orgy".

What persuaded Judge Micheli to send Knox and Sollecito to trial for murder was was the weight of circumstantial evidence against them, as well hotly contested forensic claims, including DNA traces on Ms Kercher's bra strap and on a knife found under Mr Sollecito's bed.

The couple, who had been together only for weeks, gave contradictory accounts of how and where they spent the evening when Ms Kercher was killed. Both said they had been smoking cannabis since the afternoon, which was why their memories were unreliable. After Ms Knox retraced her admission that she had heard Ms Kercher's screams, she said she had spent the night with Mr Sollecito in his flat, only going back to her own flat in the morning to have a shower and change.

But Judge Micheli found her account unconvincing, "mucking about in the house and taking a shower with all that blood [from the murder] around". He agreed with the prosecutors' contention that the crime scene had been tampered with and partially cleaned up in a successful attempt to remove Ms Knox's fingerprints. And he went along with the prosecution's claim that Ms Knox was responsible for the idea of involving Ms Kercher in a sexual game, "being the only person in a position to know that that evening Meredith would be alone in the house".

The trial will drag on in the traditional Italian way for months. This week, lawyers for Ms Knox demanded the withdrawal of a new book of sexy gossip about her, plus €500,000 in damages. The publishers, Bompiani, refused, saying the book was already in circulation. Italy already knows plenty about "Foxy Knoxy", but it is keen to learn more.