When Edda Mellas, a maths teacher in Seattle, answered the phone on November 2, 2007, she could have had no way of anticipating the world of pain she was about to enter.

In the days, weeks, months and years to follow, her lively 20-year-old daughter, Amanda Knox, a student in Perugia, Italy, would become one of the most famous women in the world - for all the wrong reasons.

Her pretty, clever daughter would be portrayed as a sexual predator who delved into orgies, drugs and fatal sex games, and would be convicted of the murder of her flatmate, Meredith Kercher, and sentenced to 26 years in prison. Her nickname ''Foxy Knoxy'' was gleefully picked up by the press.

''I didn't eat, I didn't sleep,'' Edda confides. ''I stopped functioning. I was scared. I lost 20 pounds [9kg] in a couple of weeks. It was horrible feeling so helpless.''

While Edda is in Italy as much as her teaching schedule allows, her husband Chris Mellas - Knox's stepfather - who is able to do his work online, has moved to Italy to fight for Knox's release.

And even though Edda is in tears at times during this interview, they are an upbeat, amusing couple who would be a lot of fun in different circumstances. They have had a crash course in the downside of fame, of celebrity without benefits. ''You wake up and you have satellite trucks around your house. It changed pretty much overnight,'' Chris says.

We meet in the centre of Perugia and the town is heaving. It is the famous Umbria jazz festival. There is music everywhere.

Knox is locked in a prison far outside town. But tomorrow, the defence will present to the appeal court a 125-page independent expert analysis of the DNA evidence that was used to convict her and her boyfriend, Raffaele Sollecito, who was sentenced to 25 years in prison.

This expert analysis, parts of which were leaked to the media last month, will say that the DNA evidence on the supposed murder weapon, a knife, was contaminated; and that the supposed DNA of Sollecito, found on the bra clasp of the murdered woman, was in fact vegetable matter.

Since this was evidence used to tie Knox and Sollecito to the crime, it will be a dramatic day in court - and may help expose what is increasingly looking like a shocking miscarriage of justice.

If, in the original trial, the judge had not refused the defence request for an independent analysis of the DNA, it is likely that there would not have been enough evidence to convict them, Edda says.

Once the DNA evidence is eliminated, ''there is nothing left'', she says.

''The independent experts said they ignored internationally recognised standards, the work wasn't done correctly, the results are not correct, and the procedure was not correct. They also say that it wasn't just police incompetence, that this was done with malicious intent.''

The story starts in the autumn of 2007, a time of year when the university town of Perugia is beset by excited students arriving to attend its University for Foreigners. Often they are overseas by themselves for the first time, in this beautiful medieval hill town with its own long, dark history. High-spirited behaviour is common in the many bars in the city centre. By Knox's own admission, she went ''a bit wild''.

But she was not among the typically spoilt children of the wealthy whose parents can afford to indulge them. She worked three jobs while attending university to get the money to ''expand her horizons''. And she was, according to those who know her best, very much an innocent abroad.

''Amanda didn't watch crime shows on television,'' Chris says. ''She watched The Simpsons.''

Her best friend, Madison Paxton, who has moved to Italy to support her, says: ''She was more naive than most people. She had a really beautiful life and a really beautiful family and didn't have to think the worst of people. She was very sheltered. She was painfully not a sexual predator. She was kind of a late bloomer. She was really naive about all that stuff.''

Edda adds: ''She didn't have a lot of bumps in life. Her life was schooling, softball, soccer, gymnastics, friends, rock climbing. She didn't know about the dark side of the world. She had no street smarts at all. Amanda was a white middle-class girl who never had any dealings with police and had very bland circumstances prior to this.''

Not long after she arrived, Knox was elated to find a room in a shared house that had views across the Umbrian countryside. One of the four who shared the house was the beautiful, gentle 21-year-old British student, Meredith Kercher.

At a classical concert Knox met the shy engineering student, Raffaele Sollecito, and started an affair that was mainly conducted in his apartment because his father, a wealthy urologist, paid for it and he did not have to share.

It was from Sollecito's apartment that the knife was taken and used as evidence. There was no blood on the knife but supposedly low-grade DNA of Kercher, evidence that is seriously challenged in the report.

On November 2, Knox says she arrived home at 10.30 in the morning, after spending the night at Sollecito's house, and knew immediately that something was not right. The front door was open. There was blood in the bathroom sink, faeces in the toilet. In the room of one of her flatmates - Filomena Romanelli - the window had been shattered.

Kercher's room was locked.

She died a terrible death. It is thought she was in the hands of whoever killed her for nearly two hours. She died in agony from knife wounds to the neck - her killer had sawed at her neck. She took at least 10 minutes to die.

How is it, Knox's supporters would like to know, that in the chaos of a bloody, violent murder scene there was no forensic trace of her?

In the media outcry and confusion that followed the victim was all but forgotten. The focus shifted instead to Knox, her photogenic flatmate.

On the morning the murder was discovered, a video posted on YouTube shows a dazed, shocked Knox being comforted by Sollecito outside the house. But soon she became the focus of a police theory that she was the mastermind of sex games that went wrong.

Knox and Sollecito were lusting after each other and showing no remorse, the tabloids trumpeted. Knox had written a short story about a girl being raped and murdered for a college assignment and posted it on My Space. She was seen buying underwear at a sex shop, the reports said.

''It was cheap underwear in a second-hand clothing store,'' her mother says. ''Her clothes had been locked up in a crime scene and all she had was what she was wearing.''

Knox had done cartwheels in the police station when brought in for questioning, the reports claimed.

''She was stretching,'' Edda says. ''She had been sitting for hours. The room was far too small to do cartwheels in. They took the most innocent things and twisted them.''

In her naivety, Knox had not understood that she had become a murder suspect.

''She said she went into denial because she couldn't believe this was happening to her,'' Edda says. Both Knox and Sollecito told the police over and over again that they had been in his apartment all night, cooked a meal, had a joint, watched the film Ame´lie and gone to bed.

Finally, after days of interrogation during which she was denied a lawyer, she broke down at 5.45am and signed a confession in Italian, a language she barely understood at the time. The confession went that she had been at the house with Patrick Lumumba, a man who owned a bar she worked at and was therefore on her mobile phone. This confession said Lumumba had killed Kercher while Knox was in the other room.

Knox still did not understand she was a suspect, her family says, even while 37 jubilant police officers signed her confession, cheering and clapping. This confession was later thrown out because it was obtained illegally, but it lingered in the minds of all involved. ''Case closed,'' the police had announced at a news conference at the time. Lumumba had an iron-clad alibi and was soon released, and later sued Knox for defamation.

Two weeks later came the news that DNA and fingerprints at the scene did not match Sollecito, Knox or Lumumba, but a fourth person.

Rudy Guede, from Ivory Coast, was a drifter who knew the boys who lived downstairs and had committed a series of break-in burglaries. On the run, he was picked up in Germany and sentenced to 30 years in prison for Meredith's murder, subsequently reduced to 16 years.

Since his conviction, he has changed his story many times, sometimes implicating Knox and Sollecito, sometimes saying he acted alone. In the appeal trial last month he implicated them again, though he refused to answer any questions about the crime.

In Italy, the initial trial is an inquisition and favours the prosecution. The appeal, which is mandatory, is much fairer. Last year Knox's nemesis, the prosecutor Giuliano Mignini, was tried and convicted for abuse of office in a separate case.

As the appeal began, Judge Claudio Hellman, having read the transcripts of the original trial, announced that ''the only thing we know for certain in this complex case is that Meredith was murdered''.

In prison, waiting for the interminable Italian legal system to inch forward, Knox has been studying, reading and thinking. She has become fluent in Italian. She is proficient in German and is studying Japanese, Chinese and Russian. She reads philosophy.

Edda says: ''She is an expert on existentialism. She loves reading classics. If it is an Italian classic, she wants to read it in Italian. She loves to read stuff in the original language. Her book count is literally in the thousands and thousands. A lot of it is really serious intense reading.

''We try to get her to read frivolous stuff and she just doesn't, other than Harry Potter. She has a routine. She gets up, she has coffee, she exercises, she reads, she writes letters. She exercises again.

''She translates for other prisoners. She is in a choir. She is friends with a priest who sees her regularly. She is in a guitar group. She has a phone call once a week. She has approximately two visits a week.

''She has grown up a lot. She has talked a little bit about wanting to help other people who have been wrongly imprisoned when she gets out.''

Frank Sfarzo, an Italian journalist and blogger who has followed the case in minute detail, says Knox has changed. ''Before she was a typical spoiled girl from a rich country. She was a bit insensitive at times. She was like every American girl here. Now she is a wonderful person. She has developed respect and feeling for people.''

Amanda Knox has become an industry. So far 10 books have been written about this case, a movie has been made and two more are coming.

Edda has learned a lot about the labyrinthine Italian legal system in the past four years. She has also learned the strength and ferocity of maternal love.

''You don't know until it happens to you, but I can't imagine doing anything else. And you know your child is innocent. If we had even thought Amanda had something to do with this, I am sure we would have made sure she had a good lawyer, I am sure we would have loved her and supported her, but we definitely wouldn't be screaming she is innocent and we probably wouldn't have done everything that we have done.''

Her husband is still amazed by his hitherto untapped talent for raising money - to pay lawyers.

''I never thought we could pull off anything like this. We put 'home improvements' on the loan applications,'' he laughs, shaking his head.

''That is the only way we have been able to do it. It is a hole that is so deep that I have no idea how we are ever going to get out of it.

''But it becomes a job. This is the primary job and the jobs that make the money are the secondary jobs.''

They remain cautiously optimistic that Knox and Sollecito will be released in September when the court comes back from summer holidays.

But this is Italy. They have learned that the law can be whatever the prosecution desires.

Edda says: ''Here it is like stop signs. They are there but everybody ignores them or maybe they slow down a little bit but they don't stop.''

There is a lot at stake for the city of Perugia. There will be a great loss of honour if it is found it has framed innocent kids. The prosecution will fight back vigorously.

But Edda will not stop fighting for her daughter. ''She says, 'Mum, I just want to go home.'''