Amanda Knox was seen waving a knife outside the apartment she shared with Coulsdon student Meredith Kercher, a court heard.

Albanian Hekuran Kokomani told the court in Perugia on Saturday how he witnessed American student Miss Knox, accused of murdering the 21-year-old, with the knife.

Mr Kokomani recalled seeing Raffaele Sollecito, Knox’s ex-boyfriend, and Ivory Coast drifter Rudy Guede outside the Italian apartment where Miss Kercher lived with Miss Knox.

But he could not remember if he saw all three suspects together on November 1, 2007, when Miss Kercher was stabbed to death in her bedroom.

He told the court he was driving and stopped in front of the building where he met Miss Knox and Mr Sollecito.

Mr Kokomani said he punched Mr Sollecito before Miss Knox took out a knife and threatened him.

He said: “This girl pulled out a 40cm (16in) knife from a green bag and brandished it, saying, ‘come here and I’ll show you’.”

Kokomani claimed Mr Sollecito tried to reassure him, saying “she's a girl, she’s not doing anything”.

The Albanian, who last month was arrested on drug charges, was flanked by police as he testified.

Miss Knox’s lawyer Luciano Ghirga labelled Koromani’s testimony “unreliable” but prosecutors insisted he was a key witness in the case.

Earlier in the day a homeless man, Antonio Curatolo, told the court he saw Miss Knox and Mr Sollecito in a basketball court just yards from the site of the murder at the time Miss Kercher is believed to have died.

Prosecutors allege Kercher, whose body was found on November 2, 2007, was killed during an ill-fated sex game.

They say Mr Sollecito held her by the shoulders from behind while Miss Knox touched her with the point of a knife.

Guede allegedly tried to sexually assault Miss Kercher before Miss Knox fatally stabbed her in the throat.

Miss Knox and Mr Sollecito, 25, deny wrongdoing.

Guede was convicted of murder in a separate trial last year and sentenced to 30 years in prison.

The trial continues.