Just over two weeks before the trial begins of Amanda Knox, the American student accused of murdering her British flatmate Meredith Kercher at Perugia in Umbria, a new eyewitness has reportedly come forward with evidence which if accepted would appear to cast doubt on Ms Knox’s alibi.

Ms Knox is accused together with Raffaele Sollecito, her former Italian boyfriend, of taking part in the murder and sexual assault of Ms Kercher just over a year ago, on the night of November 2, 2007. A third suspect, Rudy Guede, an Ivory Coast immigrant, was sentenced to thirty years in prison under “fast track” procedures at the end of last month for his part in the crime.

The prosecution alleges that all three took part in a sexual attack which ended with Ms Kercher being stabbed in the throat. Ms Knox and Mr Sollecito both deny the charges, claiming that they spent the night of the murder at Mr Sollecito’s flat.

They say they only arrived at the scene of the crime, the whitewashed hillside cottage which Ms Knox shared with Ms Kercher and two Italian flatmates, after 10am the next day. Ms Knox took a shower and noticed blood in the bathroom.

Their version is that they found her bedroom door locked, and that police found Ms Kercher’s semi-naked and bloodstained body when they broke the door down. However, a man who says he knew Mr Sollecito and also knew Ms Knox and the cottage by sight, has told prosecutors he saw her near the cottage at 7.45am on the day the body of Ms Kercher was discovered.

The unnamed man said: “I saw Amanda shopping at 7.45 the morning Meredith’s body was found,” according to Il Giornale dell'Umbria.

He said she was in a shop near Piazza Grimana, the basketball court and public park between the cottage and the University for Foreigners. She was “in the section where they sell detergents, though I cannot say with certainty whether she bought anything”.

The prosecution alleges that Ms Knox and Mr Sollecito broke a window at the cottage to simulate a break in by a thief, and made an attempt to clean up the scene of the crime using cleaning fluids. The witness said that, when Ms Knox left the shop, she went downhill in the direction of the cottage rather than uphill towards Mr Sollecito’s flat. He said she was wearing a scarf round her face.

Italian media reports said other new witnesses had also come forward, one of whom had reported hearing “a man and a woman arguing in Italian” inside the cottage “at about 10.30 or 11.00 on the night of November 1,” followed by an “agonising scream”.

It is not clear why the witnesses have only now given evidence.The trial of Ms Knox and Mr Sollecito opens on December 4. Both have been refused house arrest rather than prison while awaiting trial. The prosecution is to call a hundred witnesses during the trial.

They include Nara Capezzali, a woman who lives near the cottage and also claims she heard a “spine chilling scream” coming from it at about 11pm on the evening of 1 November, and Antonio Curatolo, a homeless man who claims he saw Ms Knox and Mr Sollecito “waiting for someone” near the cottage on the evening of the murder.

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