Donald Morley picked up a pillow and suffocated his wife of 69 years in a violent act his lawyer has described as a "non-voluntary mercy killing".
A prosecutor has argued the woman "did not ask to end her life ... that decision was made by the offender".
The 93-year-old husband "was distressed and unable to see a way through" when he made the decision to murder his partner when she went to bed one evening last year, a geriatrician told the ACT Supreme Court on Wednesday.
"He was faced with a choice of attending to his own medical needs in hospital and abandoning his wife, or caring for his wife and ignoring his own medical needs."
In 2023, Donald Morley killed his wife, Jean Morley, who was aged 92 and had dementia, at a Fisher home where they had lived for more than 45 years.
Prosecutor Skye Jerome labelled the act "a serious example of domestic violence where a woman has lost her life at the hands of her partner".
"It appears he did not want her to be without him."
Morley, believed to be the oldest person in the ACT ever charged with the offence, has pleaded guilty to murder.
On Wednesday, Morley faced the court via audio-visual link from the Older Persons Mental Health Unit at North Canberra Hospital.
Morley sat behind a table during court proceedings, white bandages wrapped around the top of his head, and asked at one stage, while interrupting the judge, "they look at us?"
He is under a psychiatric treatment order and has been involuntarily detained since his arrest in July 2023. He has since refused all medication and treatment.
The court heard "time is of the essence" with Morley's life expectancy estimated to be between three and six months.
Morley is terminally ill, having been diagnosed with dementia, vascular disease and malignant skin cancer which has permeated through to his skull.
His lawyer, Jon White SC, said the murder was a "non-voluntary mercy killing" and urged the court to consider a suspended sentence.
"Your honour should not compound the sad end to Jean Morley's life by imprisoning her husband who loved her so much and cared for her," Mr White told the court.
However, Ms Jerome argued an autopsy had shown Jean Morley was "a person in apparent good health for her advanced age" and did not show evidence of advanced Alzheimer's disease.
Giving evidence to the court, Associate Professor Tuly Rosenfeld said in his opinion Morley had been in "an appalling situation" and "was distressed and unable to see a way through".
"He was a 92-year-old man who knew his wife was suffering from dementia, he knew he was in trouble medically, he didn't know how to get services," Dr Rosenfeld stated.
The geriatrician was of the opinion Morley was suffering from "cognitive problems" at the time of the murder, and as a result "is a little childlike in his ability to deal with the complexity of some problems".
In documents previously tendered to the court, Morley allegedly wrote in a note found by police: "Please don't call this 'murder'-suicide."
"After 69 years married, we were both afraid of the future."
On Wednesday, Justice David Mossop raised the issue of whether the Alexander Maconochie Centre was equipped to care for the 93-year-old who would soon require palliative care.
The court heard this was a matter for the Director General of the Justice and Community Safety Directorate.
Justice Mossop is set to hand down his sentence later this month.
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