Ning Wang killed his sister and left a note for police signed "justice maker".
He then dragged 57-year-old Qin's body to the car and and drove to another sibling's home in Melbourne's east last February.
He got out, assaulted his nephew with a metal bar and told his family: "I killed my sister, she's in the boot".
Wang was acquitted of murder in Victoria's Supreme Court on Thursday, but found guilty of manslaughter.
He left two notes for police at the Clayton South home where he was caring for his 90-year-old father, Shuhuai.
One was signed "justice maker".
A second note found in the lounge room said: "Dear officers: I have killed my sister Qin at 7am to acheave (sic) my justice".
"I would like to thank you to contact my other sister ... to take care of our father. He had his breakfast at 9am."
Wang told police he was angry about being left to shoulder the burden of caring for their father, who had cancer and dementia.
He also said he felt lied to and "cheated" out of $50,000 over a long-running property dispute back in China.
"I happen to killed one of the dealy (sic) bloodsuckers," Wang wrote in another note later found in his custody cell.
Justice Rita Incerti accepted Wang did not plan to kill or seriously harm his sister.
The judge oversaw the trial alone because of the suspension of juries during the COVID-19 pandemic.
"These events and circumstances are sadly suggestive of a man of 68 years of age who was exhausted and tragically, in the moment, snapped out of frustration and anger and assaulted his sister without necessarily harbouring in that moment a murderous intent," Justice Incerti said.
Qin's body was found in Wang's boot, partially covered with an Ambulance Victoria blanket.
She had rib fractures, severe upper body bruising, a fractured eye socket and bleeding around her brain.
The judge found Qin likely died after being left unconscious and in a position that stopped her from breathing.
Wang remains in custody and will face a pre-sentence hearing at a later date.
Australian Associated Press