Ning Wang allegedly bashed his sister to death in the living room, bundled her body into his car and left a note for police, signed "justice maker".
He's standing trial for murdering 57-year-old Qin at their elderly father's Clayton South home, in Melbourne's southeast, on February 27 last year.
"Dear Officer, I have killed my sister, Qin, at 7am, to acheave (sic) my justice," Wang, then aged 68, allegedly said in one note left at the kitchen table.
Prosecutors say he left another in his father's bedroom, signing it "justice maker".
Wang's barrister, Peter Morrissey SC, agrees the man snapped and assaulted his sister.
"He just cracked without a plan because he was under extreme pressure," Morrissey told the Supreme Court of Victoria's first judge-alone criminal trial this week.
But he argued it did not amount to murder or the prosecution's alternative charge of manslaughter.
The barrister also invoked pop star Taylor Swift's song Look What You Made Me Do as well as the plot of a Dostoevsky book.
"Look what you made me do, you've driven me mad. I can't care for my dad, I can't live like this," Morrissey said of Wang's mindset at the time.
"That's how it comes about that he came to act in the bizarre way that he did later that morning."
After the alleged murder, Wang gave his 90-year-old father breakfast.
He then bundled his sister's body into his car boot and drove to his other sibling's home.
"He [then] tells anyone within earshot that he killed Qin Wang and that her body is in the boot," prosecutor Kristie Churchill said.
Wang had been exhausted after nearly three months of caring for his unwell father, and angry about a long-running family dispute as well as his sister's refusal to pitch in financially.
"The way he saw it, she [Qin Wang] had billions and all he was asking for was a drop in the ocean," Churchill said.
She also said Wang's anger, animosity, stress and lack of sleep "built up to a catastrophic incident".
Wang allegedly left another note about his sister in his custody cell which reads: "I've killed one of the blood suckers."
Morrissey sought to cast doubt on Wang's "cryptic" and "unclear" admissions to police.
He also argued Qin's injuries on their own weren't enough to cause her death, pointing to her pre-existing heart condition and asthma.
An expert who examined her body saw signs of blunt-force trauma but couldn't find a conclusive cause of death.
Closing arguments before Justice Rita Incerti are due to wrap up today.