Amanda Knox, the American student suspected of involvement in the murder of Meredith Kercher, has described her life in prison, saying she thought initially that she would "go mad" but is now "serene" after being allowed contact with fellow inmates.

Tomorrow, Claudia Matteini, the investigating judge, will hold a closed hearing at which defence lawyers for Ms Knox and Raffaele Sollecito, her Italian boyfriend, will argue that they should be released from prison and placed under house arrest instead. Ms Knox and Mr Sollecito are expected to appear before the judge in person to plead their innocence.

However Giuliano Mignini, the Perugia prosecutor, has told the judge that there are "grave indications of guilt" in both cases, and that they must be kept in prison. In Ms Knox's case, these include her DNA close to the handle of the presumed murder weapon, a kitchen knife and her blood on a tap in the bathroom of the cottage that she shared with Ms Kercher.

Both Ms Knox and Mr Sollecito can be held for up to a year before charges are brought. Ms Knox, who at one stage of the investigation admitted she was at the cottage on the night Ms Kercher was sexually assaulted and killed, will revert to her original account at tomorrow's hearing and insist that she was not, her lawyers said.

Osvaldo Napoli, a Forza Italia deputy who visited Ms Knox in her cell at the modern prison complex at Capanne, just outside Perugia yesterday, said she had told him she felt "serene".

She told him: "I have great faith in your legal system. I don't feel abandoned, I don't feel afraid. I have great faith in Italy. I'm waiting. Eveything will be cleared up."

She said that she had written a lengthy memorandum to the investigating judge in which she had stated: "I was not in that house and I am not a murderer." Mr Napoli told Italian newspapers that Ms Knox was allowed newspapers and television but switched channels when the news or programmes about the Perugia murder were broadcast.

Ms Knox has been in prison since her arrest on November 6 and was at first held in isolation with one other prisoner, an Italian woman also accused of murder. This week however she was moved to a larger cell that she shares with three other women, two Italian and one Bolivian. She has described one of the Italian women as "my second mother".

The cell, which measures 4m x 5m (13ft x16 ft), contains four single beds, "side by side as in a dormitory", whitewashed walls, a desk and a wall-mounted television. One inner door leads off to a long, narrow bathroom, and the other to a small but well-equipped kitchen. Visitors are announced by the prison guard banging on the metal door of the cell with his keys.

Ms Knox is allowed out of the cell for an hour a day to do her laundry, go to the prison canteen or chat to other prisoners. She exercises, however, in her cell, often hanging from the bars with bare hands "because it reminds me of rock climbing". On the day of Mr Napoli's visit she wore a long-sleeved, green, polo-neck sweater, navy-blue tracksuit bottoms and slippers, though she also wears jeans and trainers, according to other visitors.

La Stampa said that she emerged from Mr Napoli's description as "a pretty girl with educated manners and a little dimpled smile". This was "an image light years away from the picture painted of her by police."

Police reports based on evidence from witnesses and on statements by Mr Sollecito and Ms Knox herself have portrayed her as a cold, emotionless killer and chronic liar who habitually used drugs and brought a different man back each night from pubs and clubs to the cottage she shared with Ms Kercher.

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