Maree Mavis Crabtree, 59, was on trial in the Brisbane Supreme Court accused of killing her 26‑year‑old son Jonathan with an overdose of prescription painkillers on July 19, 2017 at the family's home before making a $125,000 insurance claim.
The jury on Monday returned its verdicts of not guilty to all charges of murder, attempt to murder and fraud after deliberating for nearly two and half days.
Crabtree held her face in her hands as the verdicts were read out and declined to comment as she left court.
Crabtree had pleaded not guilty to murdering Jonathan at the home north of the Gold Coast, and to attempting to murder him in January 2017.
Justice Martin Burns formally acquitted Crabtree and discharged her from the dock, telling the jury they had made an "enormous contribution" to society after a very difficult period deliberating.
"You have my thanks and thanks of the court and the community," Justice Burns said.
During the 19‑day trial, jurors heard competing claims that Crabtree either killed her son for financial and personal motives or was being falsely accused as part of a revenge plot by her daughter.
Defence barrister Angus Edwards had argued there were three other possibilities for Jonathan's death.
"He died of a drug overdose. We know that. He was a drug addict. Was it a suicide or accidental overdose?" Mr Edwards told the jury in his closing address.
The court heard Jonathan had tried to take his own life multiple times using different methods over several years, and his mental health deteriorated after he suffered a traumatic brain injury in a car crash.
He later became violent toward his mother and sister Tara, with Mr Edwards arguing that could have led Tara to kill him and frame her mother so she could take sole possession of their family home.
"Jonathan had a lot of demons. If he was a good person, he wasn't any more," Mr Edwards said.
In pre-recorded evidence, Tara said she watched the hallway and kitchen while her mother crushed prescription painkillers and anti‑anxiety tablets as Jonathan lay passed out in bed.
Crown prosecutor Caroline Marco alleged Crabtree wanted Jonathan dead because she feared losing the family home in a lawsuit brought by a woman affected by his robbery of a pharmacy.
Jonathan partly owned the house and, as a violent drug addict with a traumatic brain injury, could not easily be evicted, the jury was told.
The court heard Crabtree told a neighbour: "I wish Jonathan had died in the car accident. I wish he was dead," remarks Mr Edwards said had been taken out of context.
Jurors were told Crabtree had stockpiled Tara's oxycodone medication and Jonathan was found dead in his bedroom with no signs of the painkiller around his body.
The court heard Crabtree allegedly told Tara not to help Jonathan if she heard him struggling after drinking the drug‑laced smoothie, and to tell police it was a suicide.
Tara waited two‑and‑a‑half years before changing her account to police, saying she was angry at being confined in hospital for seven months.
She has been granted immunity from prosecution in exchange for her testimony.
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