Italian television has broadcast grainy images from a security camera purporting to show Meredith Kercher, the British student murdered in Perugia nearly a year ago, arriving home shortly before the murder, followed by Rudy Guede, the African immigrant accused of taking part in the killing.

However defence lawyers said that the quality of the film, taken by a camera at the open-air car park overlooking the whitewashed hillside cottage where Ms Kercher lived, was too poor to be used in evidence. The footage, broadcast by Italia Uno, one of the commercial channels owned by Silvio Berlusconi, the Prime Minister, shows a figure that may be Ms Kercher entering the cottage.

It also shows a figure identified by the television channel as Rudy Guede in a quilted jacket similar to the one Mr Guede was wearing when he was later arrested after fleeing to Germany. However lawyers for Mr Guede said that the image was so indistinct that "it could be anyone". Nicodemo Gentile, one of Mr Guede's lawyers, said: "This video proves nothing, you can't see anything, just dots".

A second pre-trial hearing is to be held tomorrow in Perugia which all three suspects — Mr Guede, Amanda Knox, Ms Kercher's American flatmate, and Raffaele Sollecito, Ms Knox's onetime Italian boyfriend — are expected to attend. At the first pre-trial hearing last week Mr Sollecito failed to appear.

His lawyers initially said that this was because he was unwell, but then said that there was no point in their client running the gauntlet of "the media circus" for a hearing largely taken up with technicalities. However, Italian media have speculated that Mr Sollecito did not want to appear in the same courtroom as Mr Guede, who in testimony to police has claimed that he saw a figure "resembling" Mr Sollecito at the scene of the murder with a knife in his hand.

At last week's hearing the judge, Paolo Micheli, granted Mr Guede's request for a fast-track trial. The trial will be held behind closed doors, with a lesser sentence for Guede if convicted. Mr Guede admits that he was the cottage on the night of the murder but claims that he is innocent and that Ms Knox and Mr Sollecito have colluded to frame him.

Defence lawyers will challenge police forensic evidence at tomorrow's hearing, saying that DNA traces found on a knife and Ms Kercher's bra strap are too indistinct to be used as proof. They will also seek to demolish the evidence of an Albanian witness who claims that he saw all three suspects at the cottage on the evening of the murder.

All three deny the prosecution allegation that they killed Ms Kercher and sexually assaulted her in a drugs-fuelled sex game which "went wrong". Luciano Ghirga, a lawyer for Ms Knox, denied reports that she would defend herself by saying that she was traumatised after being bullied at school because people thought that she was a lesbian. He said that this was "an invention", adding that Ms Knox had always said that she was not at the murder scene.

When arrested last November Ms Knox told police that she had been at the cottage and had covered her ears to block out Ms Kercher's screams. However this has been ruled inadmissible because no lawyer was present during the interrogation, and she later insisted that she had spent the evening and night of the murder with Mr Sollecito at his flat.

At last week's hearing Ms Knox adopted what Italian media called a "fresh-faced girl next door" look in an apparent attempt to convey her innocence and counteract the widespread image of her as a "killer with an angel face". The hearing was attended by Ms Kercher's parents and sister, but Ms Knox did not look at them. Her lawyers said that she had sung Beatles songs under her breath at times "to ease the tension".

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