A suspect in the murder of British student Meredith Kercher has been described as "cunning" by a court in the Italian city of Perugia.

American student Amanda Knox is being held on suspicion of involvement in the death of her flatmate at their apartment on November 2.

Kercher, 21, was found with her throat cut. Authorities believe she was trying to fight off a sexual assault when she died.

Knox, who is known as Foxy Knoxy, and her Italian boyfriend, Raffaele Sollecito, last week failed in a bid to be released from prison.

Francesco Maresca, a lawyer for the Kercher family, has now revealed some of the details of why Knox's appeal was dismissed.

In a 35-page explanation of its ruling that she should stay in jail, a three-judge panel described her as "self-assured and cunning" but also naive and with a tendency for theatrics.

Maresca said the panel's explanation was "a well-reasoned ruling that puts Amanda in the leading position in the murder."

The lawyer, who told the Associated Press news agency that he had a copy of the panel's explanation, said the judges had reasoned that Kercher was killed by someone she knew since there were no traces of a break-in.

He added: "Amanda lived in that house. She was someone Meredith trusted."

Knox has repeatedly changed her story as to her whereabouts on the night of the murder.

She originally said she was not in the apartment, then described trying to block Kercher's screams from her ears while standing in the kitchen of their flat, and has now reverted to her original story.

A native of the Ivory Coast, Rudy Hermann Guede, is also thought to have been involved in the murder.

A fourth suspect, Diya "Patrick" Lumumba, was released without charge.