A 27-year-old Perth man secretly murdered his introverted mother and then siphoned hundreds of thousands of dollars from her accounts before claiming she had killed herself in the shower, a city trial has heard.

Brent Donald Mack has pleaded not guilty to murder, with a prosecutor today labelling the accused man's story that he broke into the bathroom and found his mother, Ah Bee "Pauline" Mack, dying from suicidal wounds before leaving her there for a week with the water running as "absurd" and nonsensical.

Mr Mack, who is being tried by a judge without a jury, is accused of killing his mother in December 2008 to get his hands on money and property that was in her name after his wealthy father died that August.

Prosecutor Dave Dempster today told the trial that after killing his shy and introverted mother in the Mt Hawthorn home they shared, Mr Mack told a string of lies to cover up his crime.

He allegedly told relatives and others who had noticed a drop-off in communication and Christmas cards from Mrs Mack, 56, that she had gone overseas, moved somewhere else in Perth lo live with another man and had "psychological problems".

Statements were read out from relatives and others had also noticed the Mt Hawthorn home was becoming run-down and suddenly secured with a pad-locked fence and German Shepherd dog. They rejected Mr Mack's alleged claims before contacting police in August 2010.

Mr Mack's defence team - lawyers Sam Vandongen and Seamus Rafferty - have not given an opening address.

Mrs Mack's body has not been found and her cause of death is unknown, with Mr Dempster saying the prosecution case relied heavily on motive and the alleged lies told by Mr Mack.

Mr Dempster said that after his arrest, Mr Mack told police he had broken into the bathroom after his mother was taking a long time in the shower and found her alive but with wounds to her wrists.

"(He said to police) he understood that he was not to tell anyone about her suicide," Mr Dempster said. "He left her there in the shower and then returned shortly after, stopped the hot tap running and changed (to) the cold tap."

"He says he left the cold tap running for a week," the prosecutor said, telling the trial Mr Mack had claimed he had applied lime to the body to make it decompose faster and disposed of her at Lake Gwelup.

"Leaving his dying mother in the shower for a week... simply does not make any sense whatsoever," Mr Dempster said. "The prosecution case is that the accused killed his mother by some unknown means...to obtain her money and her property."

Records showed that Mr Mack had transferred $225,000 from his mother's bank account to his own between December 2008 and June 2010.

The money, which had included Mrs Mack's pension and income from rental investments, had been spent on living costs and start up costs for a Maylands business that the accused man had when he was arrested in 2010.

The court heard statements read from witnesses describing how Mrs Mack had lived a "miserable" life before her alleged alcoholic and controlling husband's death, and had been positive and talking about travelling before she was allegedly killed.

The trial continues.

The West Australian

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