A British student murdered in Perugia told friends that she was worried about the “strange men” that her American housemate brought back to their shared house.

Meredith Kercher, 21, said that Amanda Knox, 20, invited men that she had met in bars and internet cafés, including at least one “very strange type”, to the whitewashed hillside cottage that they shared with two Italian women, according to witness testimony leaked to Italian newspapers.

Ms Knox, her Italian boyfriend Raffaele Sollecito, 24, and Patrick Diya Lumumba, 37, a Congolese bar owner, are being held by police on suspicion of killing Ms Kercher after she refused to have sex with them. A judge is expected to rule today on whether they should be placed under formal arrest, a step towards charges being laid.

The Perugia state prosecutor’s office announced an investigation yesterday into the media leaks. Extracts from Ms Knox’s and Mr Sollecito’s witness statements have been published by Italian newspapers and testimony from Sophie Purton, 20, a close friend of Ms Kercher, also found its way into the press. Ms Purton, who is not a suspect, was reported to have told police that her account of Ms Kercher’s anxieties might be “important”.

Ms Kercher was found partially clothed with her throat cut in her bedroom last Friday. She was in Perugia studying Italian as part of her European Studies degree at the University of Leeds. Police have said that she was blameless and “morally upright”.

Claudia Matteini, a judge of preliminary investigations, presided at a hearing at the jail outside Perugia yesterday where the three suspects are being held. Legal sources said that Ms Matteini had questioned Ms Knox for three hours. The American student is reported to have written “pages and pages” of new testimony while in prison, telling investigators: “Now I remember everything.” Yesterday The Timesrevealed that police believe that Ms Knox may have been responsible for holding the victim down while one of the male suspects cut her throat.

Ms Knox had earlier denied being at the house when Ms Kercher died, and Mr Sollecito claimed that they had been together elsewhere. She then changed her story, telling investigators that she had heard screaming from Ms Kercher’s bedroom while Mr Lumumba was there, but put her fingers in her ears. She has accused Mr Lumumba of the murder and said that she does not remember if Mr Sollecito was at the house. But last night Mr Lumumba’s lawyers attacked Ms Knox as “an absolute liar” and said that her allegations were slanderous. Mr Lumumba claimed that he had not even been in the house. His lawyers, Carlo Pacelli and Giuseppe Sereni, said that their client also had an alibi. “He was never in the house of horrors, and he can prove it,” Mr Pacelli said.

Mr Lumumba admitted to Ms Matteini that he had met Ms Kercher a month before her death. This, however, contradicts his claim made at the time of his arrest that he did not know her at all.

According to Mr Sollecito’s lawyer, he was not at the scene of the crime, but was at his own home.

All three suspects were given permission to meet their relatives yesterday. Ms Knox’s mother is already in the town.

Newspapers in Perugia reported that police believe a fourth person may have been involved after the discovery of a heel imprint in the cottage and a fingerprint on Ms Kercher’s blood-soaked pillow that “do not correspond to the three suspects”.

Police are still looking for extra witnesses. Two have reported seeing Ms Knox at a launderette washing clothes and a pair of trainers after the murder.

Detectives are examining a flick-knife found at Mr Sollecito’s flat, which they say is “compatible” with the neck wound that killed Miss Kercher. They believe that the wound’s depth means that the killer must have been male. Mr Sollecito is known to have a collection of knives.

Officers have also discovered an “extensive cultivation” of marijuana in the garden of Ms Kercher’s cottage. Both Ms Knox and Mr Sollecito admitted smoking the drug that evening.

Ivo Pioppi, who owns a music shop in the city, told The Times that Mr Lumumba “is a cultured, intelligent, respectful and respectable guy. I find the accusations hard to believe.”

Yesterday Ms Knox’s Myspace profile, on which she posted a story about a girl being drugged and raped under the name Foxy Knoxy, was removed.

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