NEW details about a sex game that allegedly led to the murder of Meredith Kercher, the British exchange student, have been revealed by an Italian prosecutor.

Giuliano Mignini, the official leading the case, alleges that Amanda Knox, Kercher’s American housemate, instigated the “erotic game” and probably persuaded an accomplice into “softening up” the 21-year-old Briton.

Reconstructing the student’s final moments, Mignini alleges that Kercher’s killers became “incensed and violent” after she resisted their advances.

Knox, 21, an exchange student from Seattle and her Italian ex-boyfriend Raffaele Sollecito, 24, went on trial last Friday accused of sexually abusing and murdering Kercher in the Umbrian town of Perugia. They both say they are innocent.

Rudy Guede, 21, a drifter from the Ivory Coast, has already been jailed for 30 years for his part in the killing.

Mignini gave his account of the murder at committal hearings which were closed to the public. However, details of his reconstruction will appear in a book called Meredith: Lights and Shadows in Perugia. It is written by Vincenzo Maria Mastronardi, a forensic psychiatrist, and Giuseppe Castellini, editor of the Giornale dell’ Umbria newspaper, and will be published this week.

Mignini said Kercher, from Coulsdon, Surrey, was likely to have been irritated with Knox for allegedly bringing Sollecito and Guede to the cottage the young women shared late on the night of the murder in November 2007.

“Knox, whom Guede was always trying to please, probably pushed him into ‘softening up’ the English girl and preparing her for the erotic ‘game’ . . . while Knox ‘dedicated’ herself to Sollecito,” said Mignini.

“And when Guede failed because of energetic resistance by the victim, the three became incensed and violent.

“They grabbed Kercher by the neck and tried to strangle her. Sollecito grabbed her violently in the back and on a breast, deforming her bra clasp and then they finished her off with the violent knife stab to the left part of the neck. Kercher gave a last desperate scream, which was heard by [a neighbour].”

The prosecutor said that just before the final blow, Kercher suffered a cut to the right hand as she tried to free herself and pushed away the knife which Knox allegedly held.

A minute after the last stab wound, the three allegedly fled the cottage, with Knox and Sollecito returning later to stage a fake robbery by breaking a window, said Mignini.

The prosecutor singled out the placing of a duvet over Kercher’s body as “extremely important from a psychological point of view”. He argued it indicated pity and respect for the victim: “Amanda, especially as a woman, couldn’t bear that naked, torn female cadaver.”

Both Knox and Sollecito insist they were at his home on the night of the murder. Their defence teams dispute DNA evidence linking Knox to a knife, which investigators say may be the murder weapon, and Sollecito to Kercher’s bra clasp.

Last week Knox told her lawyer Luciano Ghirga: “At last the hour of truth has arrived. I’m not afraid. I hope that the whole truth will come out because I’ve always been a friend of Meredith’s and I didn’t kill her.”

However, Mignini alleges that on the morning after the murder Knox tried to delay the body’s discovery by telling other housemates that it was normal for Kercher’s bedroom to be locked.

When the door was kicked down, Knox and Sollecito were too far away to see into the room, where Kercher’s half-naked body lay on the floor under a beige duvet, according to witnesses quoted by Mignini at the committal hearings last October.

“When those present go outside after the body is found, Knox and Sollecito are also outside, intent on kissing and caressing each other, as they did subsequently during police searches.

“A very strange way of behaving which started the very moment the victim’s body was found . . . and at a time when all the other young people were literally overwhelmed by that discovery,” said Mignini.

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