Murder accused Amanda Knox said police threatened her with 30 years in prison if she continued to “lie” to them during questioning.

She also said a policewoman hit her twice on the back of the head while questioning her over the murder of Meredith Kercher in Perugia, Italy.

She said although it did not hurt, it frightened her.

The 21-year-old from Seattle took to the stand and spoke in fluent Italian throughout her trial as she protested her innocence.

She is accused of murdering Coulsdon student Meredith Kercher with her ex-boyfriend Raffaele Sollecito in a sex game that went wrong in November 2007. They deny charges the charges.

A Congolese drifter Rudy Guede has already been convicted of the murder and sentenced to 30 years in prison in a fast track trial.

He placed both Miss Knox and Mr Sollecito at scene.

Miss Knox said the murder was “yucky, disgusting” and compared it to an episode of the popular television series CSI.

She said she told friends it must have been a slow death because she heard Miss Kercher’s throat had been slit and from what she had seen on TV she imagined it to be slow.

She added she was very shocked by the death.

Miss Knox told the court intense questioning by the police was a “crescendo” of pressure which lead her to implicating the wrong man Patrick Lumumba for the murder.

She said she was led to believe she had forgotten things after a “steady crescendo” of “'I don't know,' 'you're a stupid liar', 'maybes', and 'imagines'”.

She told the court: "They said: 'Either you're a liar or you don't remember. Tell us the truth'."

She said she was “gutted” when she heard Mr Lumumba was in jail for the murder and said she had never had a chance to apologise to him.

He is suing her for defamation in a civil case.

When asked about her cartwheels at the police station she told the court: "Everyone deals with tragedy in his own way. I'm always trying to feel less stress. I know I may appear spacy, but that's how I am."

She said she spent the night at Mr Sollecito’s apartment where they had cooked dinner, smoked a joint and then had sex before falling asleep.

The trial has been adjourned to June 19 at which Miss Knox’s mother is expected to give evidence.