As the body of Meredith Kercher, the British student murdered in Perugia ten days ago, was returned to Britain yesterday, Italian police said that they expected to start questioning a Swiss professor who has reportedly backed the alibi of Diya “Patrick” Lumumba, the Congolese bar owner suspected of being involved in the case.

Forensic science experts are veering towards the theory that Ms Kercher was killed earlier than the original midnight to 2am estimate. Analysis of food in her stomach suggests that she died between 8.30pm and 11pm, with the fatal blow being struck about half an hour before she died.

Police said that they had found a signal “trace” of one of the mobile phones belonging to Mr Lumumba “in the vicinity of the murder scene” at 8.38pm on the night that 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.

As an alibi, Mr Lumumba has produced copies of receipts he said that he gave out when he was at the till of Le Chic, his bar. However they are timed only from 10.30pm. Police said that the unnamed Swiss professor had told them that he was willing to testify that he was with Mr Lumumba at his bar between 8 and 10 on the evening of the murder. A Senegalese man has also testifed that he was at Le Chic with Mr Lumumba, as have several other witnesses.

Further tests will take place today on the Nike shoes worn by Raffaele Sollecito, another suspect, and on a flick knife found in his possession, which is said by police to be “compatible” with the murder weapon.

And more forensic science tests are expected to take place on faeces found in the lavatory of the house where the murder took place, which police said do not belong to any of the suspects.

Police are searching for a fourth person, thought to be a North African musician, who was seen with Ms Knox at a launderette the day after the murder, washing clothes and a pair of Nike trainers. A fingerprint found on Ms Kercher’s bloodstained pillow is not that of any of the three suspects, police have also said.

Ms Kercher, a language student from Leeds University, was found dead with a wound in her throat in her locked bedroom. Amanda Knox, one of her housemates and Mr Sollecito’s girlfriend, is in custody with him and Mr Lumumba on suspicion of involvement in the sexually motivated killing.

Police have said that 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.

Edda Mellas, Ms Knox’s mother, told RAI, the Italian state television network, that her daughter had reverted to the first of at least four versions of events she has given, maintaining that she spent the entire night of the murder at the flat of Mr Sollecito.

Luciano Ghirga, Ms Knox’s lawyer, said that her “I was not even there” defence was “something she said in confidence to her mother”. There is speculation, however, that it will form the basis of an appeal against the decision by Claudia Matteini, the investigating judge, last Friday, to remand all three suspects in custody for up to a year, pending charges.

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, the newspaper La Repubblica said. On the day of the message, October 31, 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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