Traces of DNA belonging to Amanda Knox and Meredith Kercher were found on a knife at the flat of Raffaele Sollecito, Ms Knox’s boyfriend and co-accused in Ms Kercher’s murder.

Investigators said that the kitchen knife had traces of the two women’s DNA on its 8-inch (20cm) blade. Ms Kercher’s was on the tip, and Ms Knox’s close to the handle. No trace of Mr Sollecito, 23, was found. Italian media said that the DNA samples had come from blood that had been washed from the blade.

Police said it was not clear whether the kitchen knife was originally from Mr Sollecito’s flat, where it was found, or if had been taken from the cottage where Ms Kercher was killed.

Detectives had said that a flick knife that Mr Sollecito carried around with him was “compatible” with the weapon used to slash the British student’s throat, but that that knife had yielded no DNA. The reports said that Ms Knox could have cut herself while washing it, or while holding it in her fist. Investigators have tended to discount the theory that she dealt the fatal blow, because of the force involved.

New witness 'saw Meredith suspects together'

Amanda Knox, Raffaele Sollecito and Rudy Guede were see at the house in Perugia where the American student died

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• Murder in Perugia

BACKGROUND

• Meredith Kercher: Q&A

• New DNA not from Meredith suspects

• Timings crucial to Kercher murder investigation

Related Links

• US suspect in Meredith case 'turning to religion'

• Meredith: blood at suspect's flat

• Meredith suspect blames girlfriend

The discovery of the DNA traces was confirmed by Giacinto Profazio, head of the flying squad in Perugia, who described them as a significant development.

Mr Sollecito has told police that he barely knew Ms Kercher, 21, who was found seminaked with her throat cut two weeks ago. The DNA traces were discovered by police scientists who examined Mr Sollecito’s collection of knives as well as his Nike trainers, which are said to match a bloody footprint at the cottage. Traces of both Mr Sollecito’s and Ms Knox’s DNA were also found on a sponge and a cloth found at the murder scene.

Defence lawyers for Mr Sollecito expressed indignation on behalf of his family at the latest leak from the investigation. They said the forensic tests had shown no significant traces on Mr Sollecito’s trainers. He has denied being in the cottage which Ms Kercher and Ms Knox shared on the night of the murder. Ms Knox has also denied being there, but on one occasion gave police a different version in which she admitted she was present but accused Diya “Patrick” Lumumba, a Congolese bar owner for whom she occasionally worked, of carrying out the killing.

Mr Sollecito, 23, Ms Knox, 20, from Seattle and Mr Lumumba, 37, are all being held on suspicion of involvement in the killing on the evening of November 1.

Police technicians yesterday began examining the hard disk of Mr Sollecito’s computer, on which he claims he surfed the internet at home on the evening of the murder. The results of tests on hair mingled with blood found clutched in the fingers of Ms Kercher’s left hand are still awaited.

Police said that phone records showed that the phone rang at Mr Sollecito’s flat around midnight on the evening of the murder, with no answer. Records also show that Mr Sollecito’s father, a urologist in Bari in southern Italy, sent him a text message to say goodnight, with no reply.

Mr Sollecito has said he has a hazy recollection of the evening as he had smoked cannabis. He insists that he was at his flat the whole time and Ms Knox returned there at 1am.

Phone records also show that a call was made from Ms Kercher’s mobile at 10.15pm on the evening of her murder. It is not known whether the call, to a message service advising how much phone credit is left, was made by Ms Kercher, or by her killers, to give the impression that she was alive. The phone was found near to the cottage-traced by police to Ms Kercher’s flat. There they found Ms Knox and Mr Sollecito, who claimed that there had been a break-in. Ms Kercher’s body was found in her bedroom.

A local newspaper claimed that Ms Knox’s and Mr Sollecito’s fingerprints were found in the cottage. There were no prints from Mr Lumumba, who has witnesses to back up his alibi that he was in his bar, Le Chic, all evening. The fact that faeces in the shared bathroom at the cottage were not those of any of the three suspects has reinforced the investigators’ belief that a fourth person was involved.

Reports said that a witness who had contradicted Mr Lumumba’s claim that he had opened his bar “about 5.30 or 6pm” on the evening of the murder had changed his mind and now says he “cannot be 100 per cent sure”.

Italian prosecutors believe Ms Kercher was murdered after refusing to take part in an extreme sex game.

All three of the suspects have denied any wrongdoing.

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