Judy Bednar expressed fears for her safety and her son's mental health in a letter to her local MP just months before she was killed.
She also sent Labor MP Tim Richardson pictures of abusive texts from her son, Thomas Bednar, including one threatening "it won't be long until the sharks eat your flesh".
The 78-year-old was found dead in her Chelsea home in May 2021.
Her 54-year-old son is on trial charged with her murder in Melbourne's Supreme Court. He has pleaded not guilty,
Prosecutor Mark Rochford KC told the jury on Tuesday Bednar's relationship with his mother had broken down from an early age and he went to live with a foster family when he was 15.
About a year before his mother's death, Bednar began sending "delusional, aggressive, paranoid" messages to a number of people including his mother, Rochford said.
"I'm sick of my mum making out as though I'm crazy," read one June 2020 text. He threatened he would "curse" the family unless he received his inheritance.
Bednar was admitted involuntarily to Frankston hospital for mental health treatment on several occasions in 2020. He was then an outpatient at a mental health service until February 2021.
His mother changed locks in her house and installed security cameras in the months before she died. She also expressed concerns about the lack of psychiatric care her son was getting, in a letter to her local MP.
"She reported her fears for his safety and for her safety," Mr Rochford said.
"She included a picture of text messages received from him ... 'And it won't be long until the sharks eat your flesh, that will teach you for not sharing', 4th of September 2020."
Days before her death on May 4, 2021, Mr Rochford said Bednar rang his mother's doorbell and said to her: "Hello Judy, I would like to know why you lied last year and said I was crazy."
He alleged Bednar killed his mother because he blamed her for his involuntary mental health admissions.
Bednar was seen on CCTV leaving his mother's home about 6.30am on May 13, Mr Rochford said.
He said the son returned to the house two days later, where he allegedly cleaned up the scene and placed her clothes in a black garbage bag.
Ms Bednar's body was discovered during a welfare check later that day. She was naked, extensively injured and found lying between her bed and built in robe, Mr Rochford said.
She had facial injuries, which he alleged were caused by "blunt force trauma".
The trial continues before Justice Andrew Tinney.
Lifeline 13 11 14
beyondblue 1300 22 4636