A man with a vendetta, not unlike Captain Ahab's against Moby Dick, is the person who killed Melbourne mum Judy Bednar, her son's lawyer claims.
Thomas Bednar is charged with the murder of his 68-year-old mum in her Chelsea home in May 2021.
But he's not the man who did it, barrister John Desmond told the Victorian Supreme Court during his closing address to jurors on Friday.
Mrs Bednar suffered a number of blows causing significant rib fractures and died as a result of injuries that compromised her respiratory system.
She was found naked on the floor of her bedroom by police after friends were unable to reach her for several days.
Danny Cohen, who described himself as a half-brother or step-brother to Bendar, told jurors in his evidence that he had a duty of care to Mrs Bednar.
He and Bednar had fallen out over a taxi business.
Mr Desmond said a Moby Dick-like period of vendetta against Bednar had followed, in which Mr Cohen embedded himself in Mrs Bednar's life.
"The whale got Ahab, now it's Ahab's turn to get the whale," he said.
"That simple analysis is apt in this case - Bednar hurt Cohen, so Cohen was going to hurt Bednar."
He accused Mr Cohen of dressing in clothing taken from Bednar and going to his mother's house to steal $2000 in cash he knew she had in the house.
Mr Desmond suggested Mrs Bednar had awoken to find Mr Cohen there.
"He would have little time to evaluate the delicacies of the situation he's put himself in, and he assaults her," he said.
As Captain Ahab's obsession for revenge had led to his downfall, Mr Cohen's obsession with paying back Bednar had led to Mrs Bednar's untimely and tragic death, Mr Desmond said.
"Cohen may not have intended to hurt her, but kill her he did," he said.
In his closing arguments to jurors on Thursday, prosecutor Mark Rochford KC criticised the alternative suspect theory as Mr Desmond's attempting to muddy the water for jurors.
"Why is killing his mother going to bother (Bednar) in any way, shape or form? It's ridiculous, it's preposterous," he said.
He alleged Bednar's motive for killing his mother was that he believed she was responsible for four involuntary mental health admissions in the year before her death.
Bednar admitted to police he wasn't upset his mother had died, telling them she had been a "bitch" to him.
Mr Desmond acknowledged Bednar had breached an intervention order his mother took out by making a nuisance of himself - going through garbage, turning off mains power and taps.
"That undeniably caused great stress and upset and angst to Judith," he said.
"But as I've said, he walks away on every occasion without any threat of injury or killing being made. They in fact show ... a pattern of him not being prepared to physically hurt his mother."
Jurors are expected to begin deliberations on Monday.