While slaying an elderly man, Valentina Strabach faked "loud sex" to cover up the noise.
Ms Strabach, 22, is standing trial in the Supreme Court of Western Australia for the murder of South Perth man, Murray Quartermaine. It is a judge-only hearing.
The Frenchwoman has pleaded not guilty to murder on the grounds of insanity, but does not deny stabbing the 79-year-old father of four 211 times and removing his genitals in January last year.
Yesterday, two psychiatrists gave evidence in the trial of the diagnosed chronic paranoid schizophrenic. A statement written by Ms Strabach's mother was also read to the court.
Dr Mark Hall, a psychiatrist who assessed Ms Strabach's ability to plead, said she was in a "disturbed mental state" at the time Mr Quartermaine was killed.
However, he said despite her deluded beliefs she was also capable of some normal function, which may account for her admission of making "loud sex noises" to cover up the noise of Mr Quartermaine being killed.
Dr Hall said Ms Strabach was living in "two worlds" - her psychotic world and reality - and the two were confused at the time of the killing.
He said she also had no impulse control, suffered severe delusions and was hearing voices.
A statement written by Cristina Angela Callargo, Ms Strabach's mother, told of the violent childhood the young woman had endured.
Ms Callargo said Ms Strabach's father had often threatened to kill himself and his family, exposing them to severe and sustained psychological abuse.
As a result, Ms Strabach began seeing a psychologist at the age of four, continuing into adolescence.
At 15, Ms Strabach was diagnosed with depression and began smoking marijuana. Her behaviour continued to get more erratic, but her mother put it down to "a terrible teenage crisis".
Ms Callargo said at the age of 19, Ms Strabach was sexually assaulted and her condition spiralled out of control, seeing her become more reclusive and live on the street.
After she was admitted to several psychiatric hospitals in France, Ms Callargo sent her daughter to stay with family in Perth to "chill out".
However, she realised Ms Strabach's condition had deteriorated and was on a plane from Paris to Perth on the night Ms Strabach killed Mr Quartermaine.
She said Ms Strabach had been a smart and popular girl and had hated the sight of blood.
Ms Strabach's treating psychologist at Graylands Hospital, Dr Mirchea Schineanu, told the court in January 2011, Ms Strabach was still suffering from psychosis, experiencing delusions, aural hallucinations and disturbed thinking.
She also lacked insight into her symptoms, he said, and believed her deluded thoughts were reality.
The court has previously heard how police found body parts, scissors and a knife dumped in a street near the victim's home.
In a record of interview played to the court, Ms Strabach told police she had accepted a lift with Mr Quartermaine, who told her he was married and asked whether she believed people had a right to love people of any age.
She told police she thought Mr Quartermaine was a paedophile and decided to kill him.
At Mr Quartermaine's home she said she touched him but did not have sex with him. She then stabbed him on his bed with scissors.
The court heard Ms Strabach had been behaving erratically and strangely in the lead-up to the killing.
The trial continues.
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