An accused murderer's claims that he had found his reclusive mother trying to kill herself in the shower and that she wanted him to keep her death a secret was consistent with evidence and too "bizarre" to be made up, a defence lawyer said today.
Brent Donald Mack, 27, has pleaded not guilty to murder and is fighting an allegation he made up the suicide claim after killing his mother Ah Bee "Pauline" Mack in December 2008.
Mr Mack, who the court has previously found had autism but was fit to stand trial, had lived with his 56-year-old mother in Mt Hawthorn.
The Supreme Court has heard that Mrs Mack had few or no friends and her death had been undetected until 2010, over which period $225,000 had been moved from her bank account into her son's via forged cheques.
During this time, Mr Mack had told relatives and associates of his mother that she was overseas or living with a friend and did not want any contact.
Today, his defence counsel, Sam Vandongen, submitted that the evidence was consistent with his client's eventual claim to police that he had left dealing with his mother's alleged suicide too late to feel that he could be truthful about what happened.
Mr Mack repeatedly claimed to police after his arrest that his mother was alive and did not want her whereabouts known before later telling them he had broken into the bathroom after she took a long time in the shower and found her alive but with cut wrists.
He told police she had indicated she did not want help or for people to know, and that he had turned the hot tap to cold and leaving her there with the water running for about a week and burying her at Lake Gwelup wetlands.
Mrs Mack's body has not been found despite Mr Mack pointing police to where he believed her grave was.
Today, Mr Vandongen said in closing address that the evidence, including the lies and the forging of cheques, was consistent with his client's claim and was supportive of a "reasonable hypothesis consistent with innocence".
The lawyer said the case had to be seen through the "prism" of Mr Mack's behaviour, which included consistent routine and difficulty dealing with change.
The court heard evidence that Mr Mack followed a strict routine and, when confronted with change to his preferred sequence, would need time to get his around the situation.
Mr Vandongen submitted the death of his mother had left Mr Mack unable to cope immediately with the situation and then in fear of telling the truth in case he was implicated or embarrassed his mother.
"After he thought about it, it was too late to do anything about it and he was worried and perhaps ashamed," Mr Vandongen said.
The lawyer said evidence of a broken latch on the bathroom window supported his client's version of events and that Mr Mack's story was too bizarre to be made up.
"It's so bizarre that it's just not possible for it to be made up," he said, also suggesting that the forging of cheques was consistent with his client being left without his mother and needing finances.
Justice John McKechnie noted that two "relatively significant" cheques of $10,000 each were forged within in two months of Mr Mack's death. Later cheques included larger amounts.
Prosecutor Dave Dempster submitted that the suicide claim "beggared belief".
"Anyone who found a stranger in this position would do something," he said.
"It just beggars belief finding... his mother in that position he simply did nothing."
Justice McKechnie has reserved his decision to an unknown date.