After four years in jail, is Amanda Knox about to walk free?

Evidence that the student killed her flatmate has been discredited – but the final verdict is far from certain

They have already spent nearly four years in jail, but in the next few days Amanda Knox and her former boyfriend Raffaele Sollecito will learn whether they can go free, their innocence proven, or must serve out their sentences, 26 and 25 years respectively, for the murder of Knox's British flatmate, Meredith Kercher, who was stabbed at the flat the two women shared while studying in the Italian city of Perugia.

Today, prosecutors begin summing up in the couple's appeal against conviction; the verdict is expected within 10 days. Everything seems to be going Knox and Sollecito's way. Earlier this month, after two court-appointed forensic experts roundly discredited evidence which led to their conviction, Judge Claudio Pratillo Hellmann refused the prosecution's request to appoint new experts to examine it all over again. It was a dramatic turning point; even one of the prosecutors admitted that the wind had changed.

Knox, originally from Seattle, told friends that she hoped she would be home for Thanksgiving in November. Her friends and relatives have a spring in their step. Her support groups is beginning to crow.

But the outcome of the appeal is still far from certain. It is being held in the city where they were found guilty, and where Public Minister Giuliano Mignini, the chief prosecutor and the driving force behind their prosecution, continues to wield great moral and judicial power, despite being convicted of abuse of office and given a suspended jail sentence in an unrelated case in Florence.

The fate of the Knox and Sollecito rests in the hands of jurors in a profoundly conservative town, whose dubious view of the foreigners flocking to what the Italian press called "the Ibiza of foreign studies" seemed well represented by the cattolicissimo (very devout) Mr Mignini. And the prosecutor's nightmarish description of what happened the night after Hallowe'en in Via della Pergola remains welded to the case, for all the defence's efforts to dispel it.

Mr Mignini told the court in the first trial that Ms Kercher was killed at the culmination of a satanic rite. The murder was premeditated, "celebrated on the occasion of the night of Hallowe'en, a sexual and sacrificial rite", the Italian paper Il Tempo reported him as saying. The killers, he added, "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".

Ms Kercher, he explained, was on her knees in front of a wardrobe, Rudy Guede (the third person blamed for the murder and convicted at an earlier trial) held her immobile and Sollecito grasped one of her arms while Knox wielded the knife. The picture of what transpired was so clear, Mr Mignini told the judge, that "the only thing missing was a video camera".

The ghastly tableau conjured by Mr Mignini has clung to the case, and to Knox in particular, ever since. Yet he presented no evidence to support this macabre vision: no confessions, no witness accounts, no personal history of the involvement of any of the accused in such activities, above all no trace of the presence of Knox and Sollecito in the room.

All Mr Mignini possessed were the ravings of a person, well known to him, called Gabriella Carlizzi, a spiritualist blogger in Rome whose messages from "the other side" had decisively influenced a previous investigation he led. Ms Carlizzi alone claimed that both Knox and Ms Kercher, from Coulsdon, Surrey, may have belonged to a deviant Masonic sect, the Order of the Red Rose, whose rites involved human sacrifice. Again, there was no evidence of any sort for the outlandish claim.

The only forensic evidence against Knox was a knife which the prosecution claimed was the murder weapon – but it is this, along with the clasp of Ms Kercher's bra on which, it is alleged, there were traces of Sollecito's DNA, that has been the prosecution's undoing during the appeal.

This alleged murder weapon was found not at the crime scene but in the kitchen of Sollecito's flat, two weeks later. Knox's fingerprints were on the handle – not surprising as she had used it to prepare food – while Ms Kercher's DNA had been extracted, it was claimed, from minute traces on the blade. One of the unintentionally humorous moments of the first trial was when the police witness was asked how he had picked out that particular knife from several in Sollecito's kitchen. "Investigative intuition," he declared.

But now that "investigative intuition" looks as if it may be the undoing of Mr Mignini's theorem: the court-appointed forensic expert told the appeal that the trace of DNA was so weak it could be anyone's. Equal doubt surrounds the DNA alleged to belong to Sollecito and found on Ms Kercher's bra clasp, and which was not retrieved from the crime scene until 47 days after the murder.

The immediate risk for Knox and Sollecito is that the jury will discount the baffling scientific arguments of recent months and take refuge instead in the horrible yet somehow persuasive visions Mr Mignini evoked during the first trial – as well as in the lavish media coverage that preceded it – with his depiction of decadent, atheistic foreigners getting up to sinful madness while under the influence of drugs.

On the other hand, the jury may resist that temptation, overturn the convictions and set Knox and Sollecito free. In that case, however, the pair will face a different problem. If they are set free, many people in Italy, Britain and the US who have followed the case with only half their attention are likely to conclude that these two ex-students, both of them white, expensively educated and hailing from comfortable homes, have got off on a technicality; that they have finally succeeded in using their numerous advantages to twist the system their way.

Meanwhile, the only obvious victim-figure in the case, the drifter and petty drug dealer Rudy Guede, originally from Ivory Coast, languishes in jail, serving his term.

This is a tempting way to see the case, but it deserves to be laid to rest.

Amanda Knox and Raffaele Sollecito were jailed on suspicion of murder on 6 November 2007 after Knox, in an interrogation session that lasted all night, admitted being in the flat at the time of Ms Kercher's death (though she denied witnessing or having any involvement in the murder). She retracted the admission soon afterwards, claiming it had been bullied out of her by police, who had threatened and slapped her. The only evidence against her and Sollecito was the now-discredited DNA on the knife and bra clasp.

Yet Ms Kercher's room, where her corpse was found, was full of evidence, including bloody fingerprints, boot prints and DNA, all pointing unambiguously to Guede, the only one of the accused who has all along admitted to being in the flat during the murder.

That was the glaring anomaly in the prosecution's case from the outset. "If there are four people in a room and there is a big struggle and one person gets stabbed in the neck," said Lisa Lazuli, one of Knox's British supporters, "common sense tells me that there is going to be an enormous amount of blood and an enormous transfer of DNA, and it shouldn't be very difficult to tie those people to the scene."

The discrediting of the evidence of the knife and the bra clasp cuts the only thread linking Knox and Sollecito to the crime scene; there are no longer any grounds for believing they were involved. Yet, for the family of Meredith Kercher, the demise of the absurd "satanic rite" story leaves them in limbo. What was the sequence of events that night? Why did their innocent daughter have to die? For them, the anguish of uncertainty goes on.

The key issues...

Knife and bra clasp

The convictions of Knox and Sollecito depend on the claim that their DNA was found on the tip of a kitchen knife and the clasp of Meredith Kercher's bra. Court-appointed experts discredited both of the crucial claims.

Blood in the bathroom

Prosecution lawyers claim that blood in the bathroom containing the DNA of both Meredith Kercher and Amanda Knox incriminates Knox.

Her lawyers argue that it is not Knox's blood, only her DNA, and undateable, and its presence is not surprising as she lived in the house and shared the bathroom.

Time of death

Shoddy police work resulted in confusion over the time of Meredith's death. Mignini claims it was 11pm: that was when one of his witnesses said she heard a scream.

But Guede claimed the time was 9pm, which helps Knox and Sollecito because another prosecution witness claimed to have seen them at 9.30pm in a piazza in town.