In her home town of Seattle, Amanda Knox was described as a wholesome young woman — the perfect date for a high-school prom. Her friends are trying to comprehend how she could have become an alleged sexual deviant capable of a role in the murder of the British student Meredith Kercher.

When she arrived in Perugia for a three-month stay, Ms Knox, 20, was seen as an all-American sweetheart, a soccer player of note and an accomplished rock climber.

But something happened to her in those three months, according to people within the university community of the Umbrian hill town. At some point, apparently quite early on in her stay, she lost control. In the town’s seedier bars, she soon became known as someone who was capable of intense jealousy and rage. She dedicated her free time to the drink, drugs and easy sex of Perugia’s nightlife.

As she contemplates spending up to a year in an Italian jail awaiting charges — she was detained yesterday along with her Italian boyfriend, Raffaelle Sollecito, 24, and Diya “Patrick” Lumumba, 38 — those who knew her spoke out. One acquaintance said that Ms Knox had not been corrupted by any particular person because she was “already up for it”. She had plunged fresh from Seattle into a world of vodka, marijuana and free-and-easy sex. According to Mr Sollecito’s statement to police, she went to bed with him the day they met and, according to leaked testimony, she was known to pick up men in the bars and internet cafés. Ms Knox is thought to have “befriended” at least one North African man.

Acquaintances confirm the report of Ms Kercher’s friend, Sophie Purton, that Ms Kercher had been alarmed by the men whom Ms Knox brought home, including some “strange types”.

This is not the woman her friends in the US know. Dominick Balsoma, 21, told The Times that Ms Knox was his first date and perfect for his high-school homecoming dance. She was, he said, a good student and sportswoman. They were educated together at the private $12,000-a-year Jesuit-run Seattle Preparatory School, where pupils recited daily prayers and adhered to a strict dress code. She played an orphan in a school production of the musical Annie, and was popular among her peers. “She was always smiling. The last time I saw her, she was very excited about going to Italy,” he said.

Mr Balsoma said that they had stayed friends and had attended the University of Washington together. She e-mailed him only a few weeks ago, he said. He was surprised to learn that she had posted a short story on her MySpace page describing the rape of a girl. In the story, Baby Brother, a man called Edgar asks his brother, Kyle, whether he carried out a rape with a drug called “hard A”.

Mr Balsoma said: “Normal people can write horror stories, but it does suggest a side of her that might not have been public. It is possible that she fell in with the wrong crowd, but I cannot believe she could have been involved with that crime . . . she is just not a violent person.”

In Perugia, locals have told The Times that their town has two faces, both of which appear to have seduced Ms Knox. For tourists and second-home owners it is an idyllic Umbrian hilltop town, the home of the Renaissance painter Pietro Vannucci, nicknamed Perugino, and many Etruscan, Roman and Renaissance treasures. The historic centre of Perugia has long had pubs and bars, but joining them are internet cafés and kebab houses to cater to a multracial, multicultural population of students and immigrants. “Perugia is Italy’s Ibiza,” said the newspaper Corriere della Sera this week.

It is a heady cosmopolitan atmosphere for the young (Ms Kercher was about to turn 22 and Mr Sollecito is 24) but many of the “hangers-on” in the student culture are older. Mr Lumumba, the man Ms Knox accuses of murdering and sexually violating Ms Kercher, is 37. He denies that he was at the “house of horrors” at all, and claims that he can prove it.

He certainly knew Ms Knox well, however, because she worked for him at Le Chic, the bar he recently acquired in the centre of Perugia, helping him to serve customers on Tuesdays and Thursdays.

One theory is that Ms Knox, described by acquaintances as jealous of other attractive women, fell out with Ms Kercher because she had told friends that she, too, wanted to help out at Le Chic. “There are a lot of older men who hang around the student community,” said Mirko Palmesi, an Italian-Canadian who recently left Perugia after studying at the University for Foreigners. “I used to ask myself all the time what these older types were doing with us.”

Mr Lumumba came to Perugia because it houses the University for Foreigners, an institution set up in the 1920s to encourage the study of Italian language and culture. Unlike most students, however, he stayed on and made a living as a reggae musician and barman, becoming a well-known figure in Perugia’s night life.

Did he wield a malign influence over the youngsters, leading them into a life of sex and drugs? Not according to those who know him. They said that he was a “gentle soul, respectful and respectable” with a Polish wife and baby son.

Some Italian locals claim that American students cannot cope with the alcohol. Unlike Italy, the US prohibits the sale of alcohol to under 21s. A bus stop near Ms Knox’s home is plastered with posters advertising “buy one, get one free” deals at pubs and bars during happy hour. “We start drinking about six and just carry on,” one student commented. “It is perfectly normal.

“These foreign kids tend to have a lot of money in their pockets,” said Ivo Banella, a trade union official in Perugia. “By local standards they are rich kids, with cash from their unsuspecting parents, who have no idea what their children get up to here.” Joints are openly smoked even on the Cathedral steps and hard drugs change hands in dark corners.

Drugs remain at the heart of the case. Marijuana was grown by the students at the whitewashed cottage Ms Knox and Ms Kercher shared with two Italian girls and Ms Knox and her boyfriend admitted smoking on the evening of the murder, which they claim accounts for their confused accounts and memory lapses.

On the ten-minute walk from the University for Foreigners to the cottage where Ms Kercher was killed is a grim municipal park and basketball court, which even during the day is haunted by homeless migrants and by young dealers.

Some foreign students are planning to leave. “I am going back to London,” said Lina, one of Ms Kercher’s fellow students from Leeds University. “I am taking a break. We are all scared and shocked.” Would she come back to Perugia? “I’m not sure. It is a great place, but I’m not sure”.

Meanwhile, the young American woman at the heart of the mystery sits in an isolation cell in the new prison outside the town, far from the nightlife she used to take part in.

According to prison sources, she is calm and controlled, refusing to answer questions but writing page after page of her version of events that fateful night — the latest in a line of changing stories full of inconsistencies and contradictions.

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