A witness at the Meredith Kercher murder trial on Friday told a Perugia court how she heard a scream followed by two sets of footsteps on the night the British exchange student was killed.

Neighbour Nara Capezzali said she had woken up at around 23.00-23.30 to go to the bathroom on the night of November 1, 2007 when she heard a ''prolonged woman's scream'' which she described as ''not normal''.

''It made my skin crawl,'' said Capezzali, who imitated the sound she had heard in court.

''Every time I go past that window (in my house) I hear it again''.

The witness said after the scream she had ''heard running on the metal staircase'' near Kercher's house and ''almost at the same time'' footsteps in the gravel and dry leaves in the square opposite the house.

However, under questioning Capezzali said she could not be sure of the date of the scream.

American student Amanda Knox, 21, and her Italian former boyfriend Raffaele Sollecito, 25, are on trial for the murder.

Exchange student Kercher, 21, was found semi-naked and with her throat slit on November 2, 2007 in the house she shared in Perugia with Seattle-born Knox and two Italian women.

A third defendant, Ivory Coast national Rudy Guede, 21, was sentenced to 30 years for sexually assaulting and murdering the British exchange student at a separate trial in October.

The prosecution claims Kercher was killed when all three defendants tried to force her to participate in ''a perverse group sex game''.

The defendants deny wrongdoing.

Guede's lawyers, Walter Biscotti and Nicodemo Gentile, were in court to hear Capezzali testify Friday and said her evidence verified Guede's continued claims of innocence.

Guede has always admitted to being in the house when Kercher was murdered, but said he was in the bathroom when the killing took place.

He claims he emerged to find two people in the house who then ran away, and that he attempted to help the dying Kercher before panicking and also fleeing the scene.

''Capezzali said she clearly heard two people running away on the night of the murder, one in one direction and another in the other,'' Guede's lawyers said.

''It's a version of events that tallies perfectly with Rudy's claim that while two people ran away he was helping Meredith''.

The trial of Knox and Sollecito, which began in January, is being held in stages and is expected to continue until the summer.