A woman accused of murdering her adult son by giving him an overdose of painkillers did so to rid herself of a "troubled young man", a court has heard.
Maree Mavis Crabtree, 57, faced Brisbane Supreme Court on Monday and pleaded not guilty to one count of attempted murder, one count of murder and one count of attempted insurance fraud.
Jonathan Crabtree, 26, was found dead at 9.55am on July 19, 2017 in the family's home at Maudsland, north of the Gold Coast, with an excessive amount of prescription oxycodone in his system.
Crown prosecutor Philip McCarthy told the jury in his opening statement for the trial he would endeavour to prove Crabtree deliberately administered a drink to her son containing the oxycodone that killed him.
"Jonathan's younger sister, Tara, will tell us of her mother's plan to kill her brother. She will tell us, frankly, that she helped her mother," Mr McCarthy said.
Mr McCarthy said Tara would testify that she stood lookout while Crabtree mixed the drink and she heard Jonathan struggling to breathe during the night after he drank it.
Crabtree was also accused of attempting to murder Jonathan in a similar manner on January 10, 2017.
Mr McCarthy said the jury would hear testimony from a pharmacist that Crabtree would always collect prescriptions on Tara's behalf.
Mr McCarthy said Jonathan had a brain injury as a result of a car crash and his mother found his behaviour difficult and abusive.
"He was a troubled young man, he used drugs and required significant physical care," Mr McCarthy said.
The jury also heard claims Crabtree believed Jonathan's alleged armed robbery of a chemist five years ago would lead to a lawsuit and cost the family its house.
Mr McCarthy said Crabtree told a family friend in early 2017: "Jonathan is like a potato, he has no life and I just want to put something in his drink so he just won't be here".
Crabtree told police during an interview her son had been depressed, addicted to prescription medication and taking "anything he can get his hands on".
Mr McCarthy said Crabtree told police Jonathan tried to kill himself in 2015.
Crabtree was also accused of trying to access $100,000 in Jonathan's disability insurance payout.
Defence barrister Angus Edwards said the possibility Jonathon was deliberately given a fatal dose of oxycodone via a fruit smoothie from Marie Crabtree relied on a single witness.
"That possibility is based on a story Tara Crabtree came out with two years after her brother died," he said.
Mr Edwards told the jury the whole trial was about whether they believed Tara's story was honest and consistent with independent evidence.
Mr Edwards said Crabtree's statement's about Jonathan while dealing with his violent behaviour had been "cherry picked" and it was possible he had accidentally or deliberately taken an overdose of drugs.
The trial is due to run for three weeks before Justice Peter Davis.
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