Refusing their lawyers' request for bail, Judge Claudia Matteini cited police evidence that Amanda Knox, 20, Raffaele Sollecito, 24, and Patrick Lumumba, 37, might have been planning their escape when they were arrested on Tuesday morning on suspicion of murdering Meredith Kercher, a 21-year-old student from London who was studying for a year at the University of Perugia.

Judge Matteini ordered Knox, the American flatmate of Kercher, and Sollecito, the Seattle student's Italian boyfriend, to be held in custody for up to a year, pointing out that Sollecito had unsuccessfully tried to fool investigators by buying a new mobile phone the day after the murder.

Lumumba, a Congolese musician and bar owner, was also ordered to remain behind bars.

All three have denied involvement in the killing.

But fresh details emerging this weekend from the official report by Matteini, the preliminary judge in the case, revealed detectives believe they have solid evidence to back up their suspicions.

There was no doubt, Matteini wrote, that the murder weapon was a pocket knife owned by Sollecito, which he told police he always carried with him. He is said to have collected knives and to be fascinated by them.

His girlfriend of two weeks, Knox, the expensively-educated American known as 'Foxy Knoxy' on her MySpace profile who lived with Meredith Kercher, was also implicated by fresh forensic evidence that showed she may have held her "friend" still while her throat was slit.

The three wounds to Kercher's throat were probably the result of threats intended to make her comply with the wishes of her assailants, said Judge Matteini, revealing she had been injured on the neck twice before the fatal cut, when "the blade penetrated deeply, causing the fatal wound".

She said evidence presented by police convinced her Kercher had suffered sexual violence before she died and that her resistance to the attack "is obvious from objective data."

'The case is closed' The third suspect, Patrick Lumumba, told the judge during Thursday's closed hearing that he was working normally in his bar throughout the evening of 1 November.

He admitted exchanging text messages with Knox, who worked casually in the bar, Le Chic, but claimed they were innocuous.

If the judge largely confirmed the boast of police chief Arturo de Felice that "the case is closed", there remains the spectre of a fourth person who may have been involved in the crime, if only helping to clean up.

Unidentified prints have been found in the murder room, and police are following up reports of a suspicious person who was seen washing clothes and Nike trainers in a launderette used by students.

Italian law allows judges to jail suspects without charging them if there is sufficient evidence and a chance they may flee, carry out another crime or interfere with evidence. All three suspects will be held in isolation.

The judge's ruling document refers to allegations made by investigators that our correspondent described as "explosive".

These include claims that:

>> A 3.3in (8.8cm) flick blade belonging to Sollecito is compatible with the stab wound in Kercher's neck.

>> Traces of three footprints in blood found in the victim's room match the imprint of shoes belonging to Sollecito.

>> Kercher fought off a violent attack and had been raped.

Police allege Lumumba entered Kercher's room to have sex, during which something went wrong.

They believe Sollecito went in to join them and pulled out a knife.

According to the case presented by investigators, the suspects have all changed their stories. They said Knox had an unscrupulous tendency to lie repeatedly.

All three suspects have denied involvement in the killing, but officers have said they are confident they can place the trio at the scene.

Police have said Knox crumbled under interrogation, and now admits having been in the next room when Leeds University student Kercher was murdered last week, but covered her ears to her flatmate's screams. Knox has blamed Lumumba for the murder.

But Carlo Pacelli, Lumumba's lawyer, said that his client had 16 alibis . . . including one from a university professor . . . who could place him in his bar at the time of the murder.

Suspects lied to police Pacelli added that Knox was lying and that Lumumba had "slept soundly" for the previous two nights.

Lawyers for Sollecito have admitted that he lied to police, saying he was at a party on the night of Kercher's death.

He has since said he was at his own home with Knox at the time.

Knox's lawyer said she had had nothing to do with Kercher's death and should be freed.

Kercher's body was found in her bedroom on Friday morning in a pool of blood.

Police do not believe the murder was premeditated, but they allege each of the suspects played a role.

Crucial to the case will be the suspects' phone records and calls they exchanged after the murder.

Lumumba had been in the country since 1988, while Sollecito was a student at the local university. Knox is from Seattle, Washington.