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.
