Amanda Knox, the American student suspected of involvement in the murder of her flatmate Meredith Kercher in Perugia, broke down and cried during questioning when asked how she could possibly know so much about Ms Kercher's "death agony" if she was not there.

Ms Knox, questioned yesterday by Giuliano Mignini, the chief investigating magistrate in the case, broke down again - this time "hysterically", with "shaking fits" - when asked why she had accused Diya "Patrick" Lumumba, a Congolese bar owner in Perugia for whom she worked part time, Italian reports said today. Mr Lumumba was arrested but later released for lack of evidence, although he remains "under investigation".

The chaplain at the prison where Ms Knox, Raffaele Sollecito, her Italian boyfriend, and Rudy Hermann Guede, an Ivorian immigrant, are being held, had earlier said she was "prepared to tell the truth". Although she has at times in the past admitted she was at the cottage she shared with Ms Kercher, during the six hour interrogation she insisted on her original claim that she was at Mr Sollecito's flat all evening and all night.

Asked how she explained the presence of both hers and Ms Kercher's DNA on the kitchen knife thought to be the murder weapon, Ms Knox replied "I don't know, I can't understand it". She said "Mez" - Ms Kercher's nickname - had never been at Mr Sollecito's flat, where the knife was found. Il Messaggero said she appeared unaware that Mr Sollecito has claimed that he, Ms Knox and Ms Kercher had cooked together in the kitchen of his flat.

Mr Mignini reminded Ms Knox that when first questioned at Perugia police station as a witness the day Ms Kercher's body was discovered, she had told other witnesses she had seen Ms Kercher lying next to the wardrobe with a wound to her throat which had cause her to die "in slow agony". She had given a similar description of the scene to Marco Zaroli, the boyfriend of Filomena Romanelli, one of two Italian female students who shared the cottage with Ms Knox and Ms Kercher.

Although Ms Kercher's body was found on other side of the bed, police forensic scientists have concluded that it was dragged there, and that she was in fact murdered in front of the wardrobe by having her throat slit while on her knees. Asked how she could have known this if she was not there, Ms Knox began to cry and refused to reply.

She appeared similarly "confused" when confronted with the testimony of Robyn Butterworth, one of Ms Kercher's fellow British students at Perugia, who said that at the police station Ms Knox had appeared "strangely unmoved" by Ms Kercher's death and "proud" of having "found" the body. Her lawyer said Ms Knox had "exercised her right not to speak" for the rest of the interrogation.

Police believe Ms Knox accused Mr Lumumba to cover up for Mr Guede, the third suspect in the case, whose bloody fingerprints were on Ms Kercher's pillow and who has admitted being at the cottage during the murder while denying he committed it himself. Sources close to the investigation said it was striking that Ms Knox never mentioned Mr Guede at all, "as if he did not exist", when in fact they knew each other and had exchanged mobile phone calls before and after the killing.

Mr Guede's situation appeared to worsen at the weekend after it emerged that traces of his DNA had also been found on the fasteners of Ms Kercher's bloodstained bra. Police said it appeared the bra had been ripped off. After the killing Mr Guede fled to Germany, where he was arrested and extradited back to Italy.

Corriere della Sera reported that Edda Mellas, Ms Knox's mother, and her former husband Kurt, Ms Knox's father, were having problems finding rented accommodation in Perugia because "no-one wants to rent to anyone linked to the Meredith Kercher case". Ms Knox's parents, who have vowed to stay near their daughter until the case is resolved, are at present lodged in the village of Mantignana, near Lake Trasimeno, 15km from the town.

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