Gabrielle Woutersz trial: Drugs drove daughter to mother's Canberra killing

Gabrielle Woutersz, 25, is accused of murdering Norma Cheryl Woutersz, 56, in October 2014.

It's alleged Woutersz fatally cracked her mother's skull with a hammer before trying to bury her body in the backyard of their Dunlop family home.

Her father arrived home to find his daughter inside the house and his wife's body tied to a ladder beside an emptied planter box.

Woutersz pleaded not guilty to murder. Her month-long ACT Supreme Court trial heard from its final witness before lawyers began their closing submissions on Monday.

It is not disputed that Woutersz killed her mother.

Prosecutors have argued throughout the trial Woutersz's state of mind at the time of the killing was linked to her extensive past use of drugs, mostly ice, while her lawyers say she had a mental illness that qualified her for a defence of mental impairment.

In his closing submissions, prosecutor Shane Drumgold said Woutersz's family, largely in denial over the accused's drug use and trying to make sense of her deteriorating mental state, had also blamed her mental illness for Mrs Woutersz's death.

"We say all of the evidence points the other way, points to drug use," he said.

But while defence barrister Bernard Collaery described the killing as "chaotic", "horrific", "bizarre" and "almost ritualistic", he questioned whether there was any evidence Woutersz was intoxicated at the time.

Mr Drumgold argued Woutersz knew what she was doing when she attacked her mother, knew that it was wrong, and had actively pursued a mental impairment defence in the months after the killing.

He pointed to Woutersz's significant clean-up of the crime scene and attempts to hide her mother's body, as well as a phone conversation the day of the alleged murder when she told a cousin, "I f---ed up".

The court heard Woutersz had a long history of drug use, which began as a teenager, and continued during her time as a sex worker interstate, and had often experienced psychotic symptoms.

Mr Drumgold acknowledged the case was tragic and emotional, with many victims, but urged jurors to put their emotions aside and answer legally-defined questions using the evidence.

He said they should see the killing as the effect of drugs.

"We say she's a victim whose drug use saw her fall from a loving daughter and prize-winning personal trainer to a girl who couldn't hold down a job as a sex worker.

"No-one wants to believe a young girl could fall so low, culminating in the tragic death of her mother."

Mr Collaery, at the start of his closing submissions, challenged the prosecution's suggestion Woutersz was "a damaged ice addict" and said six experts had been consistent in their diagnosis of schizophrenia or schizoaffective disorder.

"Can you attribute all her behaviour to drugs?" he asked the jury.

"Do schizophrenics get into risk-taking behaviour such as she has – prostitution and drugs – because it's an effect of the illness?

"Drugs could be an attribute of the illness, not the reason for psychosis."

Mr Collaery said there was no direct evidence Woutersz had taken drugs after early September 2014, more than a month before the killing, and the evidence indicated she had been "a seriously ill young woman" when she attacked her mother.

Woutersz has not given evidence during the trial.

Mr Collaery will continue his submissions before Chief Justice Helen Murrell on Tuesday.