Italian police say they have uncovered new evidence calling into question the alibi of Diya "Patrick" Lumumba, the Congolese bar owner suspected of involvement in the alleged attempted rape and murder of Meredith Kercher, a British exchange student, in Perugia ten days ago.

As forensic experts veer towards the theory that Ms Kerchner was killed several hours earlier than the original midnight to 2am estimate, police said they had found a signal "trace" of one of the mobile phones belonging to Mr Lumumba "in the vicinity of the murder scene" at 8.38 pm on the night she died. They were also conducting tests on a "sweat soaked T-shirt" belonging to him, and on "medium length" hair mixed with his own hair.

Ms Kerchner, a Leeds university language student, was found dead with a wound in her throat a week last Friday, in her locked bedroom in the whitewashed cottage in Perugia that she shared with three other women - including US student Amanda Knox, who is in custody on suspicion of involvement in the sexually motivated killing.

Initial reports that Ms Kercher died between midnight and 2am on November 2 have been revised to suggest that the knife attack took place earlier and that Ms Kercher, whose throat was cut after "sexual activity" which police believe was an attempted rape, was then left slowly to bleed to death after a long agony.

Analysis of food in Ms Kercher's stomach show she died between 8.30pm and 11pm on 1 November, with the fatal blow struck around half an hour before she died, investigators say.

As an alibi, Mr Lumumba has produced copies of receipts which he says he gave out when he was at the till of his bar, Le Chic. However they are only timed from 10.30pm onwards.

Police have traced a Swiss professor who was staying a a hotel in Perugia last week and is willing to testify that he was at Mr Lumumba's bar between eight and ten on the evening of the murder. It is not clear however whether he will confirm that Mr Lumumba was at the bar the whole time. A Senegalese man has also testifed he was at Le Chic but has said he does not remember what time he arrived or how long he stayed.

The dead girl's body was today being flown home to Britain for burial, after lawyers for Mr Lumumba tried unsuccessfully to have it held in italy for further forensic tests to clear up "confusion" over the time of death. The coffin was sent from the morgue at Perugia to Rome airport, where after a delay of a few hours it was put aboard an Alitalia flight due to land at London's Heathrow airport at 3.25pm today.

Police say mobile phone interceptions are crucial to the investigation. Ms Knox sent a text message to Mr Lumumba on the evening of the murder apparently arranging to meet. She and her boyfriend Raffaele Sollecito, who is also in custody in relation to the crime, then both turned off their phones off on night of murder only to turn them on again the next morning, while Mr Lumumba switched to a different sim card.

Police said Mr Sollecito had been heard in an intercepted phone call telling his father Franco, a respected urologist from Bari, that "those stupid policemen" had failed to find the three inch flick knife he carried in his jeans when he was first questioned.

The knife was confiscated in a later interrogation, and is almost certainly the murder weapon, according to police. Dr Sollecito said, after seeing his son in prison: "Everyone has a hobby. I collect guns, my son has a passion for knives". He said his son told him "Papa, you have to believe me, I'm innocent".

However an apparently sinister text message received by a man in Rome the day before Ms Kercher's murder, reading "For me, Meredith dies tonight", might have an innocuous explanation, said the newspaper La Repubblica. The day of the message, 31 October, Italian TV was due to broadcast an episode of the medical soap opera "Grey's Anatomy" in which the heavily advertised plot twist revolved around the possible impending death of Dr Meredith Grey, the main character.

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