A man has been jailed after bludgeoning his elderly mother to death in the belief it was a sacrifice to prevent her suffering as the world was ending.
Gary Allan Giles pleaded guilty to manslaughter after he killed his mother Gloria McMaster at her Mango Hill home, a suburb north of Brisbane, in 2018.
The now-56-year-old had been treated for mental health issues for more than a decade and was admitted to hospital twice for care.
Giles moved from NSW to Queensland in 2017 to help care for his mother as her health was deteriorating but their relationship, albeit close, became toxic, a court has been told.
Months before the crime, Giles stopped taking his anti-psychotic medication because he thought his mental health had improved, which led to escalating delusions.
Giles believed the end of days or Armageddon was approaching so he resolved to kill himself and his mother to spare them from suffering.
In August 2018, Giles went into Ms McMaster's home as she lay in bed, believed to be asleep, and struck her five times to the head with a hammer before he slit her wrists with a knife.
"The attack was vigorous and brutal," Justice Melanie Hindman told Brisbane Supreme Court during sentencing on Friday.
Giles also harmed himself before calling the police.
He was initially charged with murder but it was downgraded to manslaughter with Justice Hindman sentencing him based on diminished responsibility due to his mental health.
"Your mental illness amounted to an abnormality of the mind which substantially impaired your capacity to know that you should not have done what you did," she said.
In notes recorded by a fellow prisoner, Giles admitted he killed his mother to "transition her to heaven to avoid the end of days".
Giles' extreme religious views have prevailed during his six years in custody as his niece said he continues sending letters to the family disapproving of their non-religious lifestyles.
"He constantly wants us to take salvation by accepting Christianity and believes we will be condemned to hell without doing so," Amy Drysdale said in a statement to the court.
"Having been berated with these views for years, it makes us fearful that should he be released, he could easily snap and be his next target.
"There are multiple times throughout his life where he has stopped taking his medication, and this has resulted in multiple psychotic breaks, the most recent the murder of my nan."
Ms Drysdale said: "I am still scared of Gary Allan Giles."
"Until he dies, I will forever live in fear for myself, my mother, my brother and my father."
Justice Hindman sentenced Giles to 11 years in prison.
"The offending was very serious. Ms McMaster was a vulnerable senior citizen, she was in her own home, she was in her own bed.
"She was killed in a horrifically violent manner. It can only be hoped that she did not suffer."
Giles will be eligible for parole after serving 80 per cent of his sentence with 2248 days in custody considered time already served.
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