Ning Wang is charged with murdering his 57-year-old sister, Qin, at the family's southeast Melbourne home in February 2019.

"Dear officer, I have killed my sister Qin at 7am to acheave (sic) my justice," the 68-year-old allegedly said in a handwritten note found at the Clayton South kitchen table.

Prosecutors say Wang left a second note asking that his 90-year-old father, who had health problems including dementia, be looked after. It was signed "justice seeker".

Wang is facing the Supreme Court of Victoria's first judge-alone criminal trial, after juries were suspended because of the COVID-19 pandemic.

He gave his father breakfast after the alleged murder, then put his sister's body in the boot and drove to another sibling's house.

"I have killed my sister, she is in the boot of the car," he allegedly told police called by the family.

In a police cell, prosecutor Kristie Churchill said Wang left a third note saying: "I've killed one of the bloodsuckers, only one of many. It is a shame".

She said Wang had been angry about an ongoing financial dispute in the family as well as conflict about the care of their father.

Wang admitted assaulting his sister but did not intend to kill or seriously harm her, Peter Morrissey SC argued.

The defence lawyer said Wang "just lost it" under the strain of caring for his father "in very stressful circumstances".

Mr Morrissey added the assault wasn't severe enough to cause Ms Wang's death. She had a heart condition and asthma.

None of the notes found by police amounted to an admission of murder, the lawyer also said.

He asked Justice Rita Incerti to find Wang guilty of manslaughter instead.

The trial is due to continue on Thursday.

Australian Associated Press