Daughter who chopped off her mum's head during a kitchen fight had a 'crush on' meat worker who she bombarded with 100 calls a day and threatened to flush his wife's head down the toilet

A Sydney woman who chopped off her mother's head also bombarded a man with up to 100 calls a day and then threatened to flush his wife's head down a toilet, a court has heard. 

Growing increasingly agitated with threats from her mother she would be put back into a mental institution, Jessica Camilleri 'saw red' in July of 2019.

The now 27-year-old told Professor David Greenberg she was in a 'fit of rage' when she dragged her mother by her hair down the corridor before opening up the knife drawer 'to scare her'.

'I think I had sick thoughts. I used to watch horror movies. I got it off horror movies,' she told him.

The NSW Supreme Court also heard Ms Camilleri 'relentlessly' pursued a married man who owned a local meat business, ringing him up to 100 times a day before threatening to kill the man's wife.

Jessica Camilleri (pictured above) 'saw red' in July of 2019 when her mother threatened to send her back to a mental institution 

Rita Camilleri (pictured above) was stabbed at least 100 times in the frenzied attack which saw her decapitated

Following a brutal attack, Rita Camilleri's head was found outside on the footpath, while her blood-drenched body was on the kitchen floor near her eyeballs, tongue and tip of her nose.

An autopsy found she had been stabbed at least 100 times and had suffered more than 30 defensive type wounds on each hand.

Ms Camilleri has pleaded not guilty to murdering her mother at their St Clair home in Sydney's west in July 2019.

Both the prosecutor and defence barrister agree Ms Camilleri stabbed her 57-year-old mother, her sole carer.

The jury must decide whether the charge can be reduced to manslaughter with the partial defence of being 'unable to control her actions due to a substantial impairment of the mind.'

The crown witness told the NSW Supreme Court on Thursday that Ms Camilleri, who suffers from complex psychiatric disorders and autism spectrum disorder, stopped taking her medication six months before the attack.

She also told Dr Greenberg about developing obsessive crushes on men she would randomly ring, including local business owner Matthew Layfield who at one point she 'relentlessly targeted' along with his employees.

Mr Layfield owned a meat business in 2019 when the phone calls started and would 'turn ugly' whenever someone tried to end the conversation.

Detective Sergeant Grant Gilbert read out Mr Layfield's statement about the harassment that lasted two months.

The gruesome St Clair murder scene (pictured above) where Jessica Camilleri decapitated her mother Rita Camilleri in July of 2019

'I will stab you and cut your head off with a knife'. It always ended like that, it did not matter who she was talking to,' the statement read.

Mr Layfield made regular contact with Ms Camilleri's mother who said her daughter had developed a 'huge crush' on him after seeing his photograph on the company's website and would 'go crazy' when she heard his voice.

After Mr Layfield's friends and family members - including his wife - were also targeted with similar threats of beheading, he contacted Rita Camilleri saying 'something needed to happen'.

At her wits' end, the 57-year-old burst into tears and said she did not know how to control her daughter anymore. 

She had previously confiscated her phones and disconnected her service. 

The trial continues with more evidence from Dr Greenberg on Friday.