Lawrence Michael Duca was convicted by a Supreme Court jury in March of murdering The Phuong Vuong in the furtherance of a violent crime - shooting the dressmaker twice before robbing his home in June 2017.

"He could not have paid a bigger price for his drug use," barrister Theo Alexander said of Duca's long battle with drug addiction.

Prosecutors have argued Duca's drug history is an aggravating circumstance to the murder.

Duca and another man robbed Mr Vuong in his Deer Park home, arriving with a 12-gauge shotgun and a plan to steal valuables.

Mr Vuong, a sewing machinist who also ran a massage service, was in charge of a money pot known as a "hui" collected from his local Vietnamese community and distributed monthly.

He tried to fend off his attackers and was fatally shot in a struggle at his front door.

Duca and the other man made off with $27,000 cash, a Louis Vuitton bag and a wallet.

Dr Alexander argued at trial Duca was not the shooter.

Mr Vuong's body was found 10 days later by a friend.

The jury could not reach a unanimous decision on common law murder and Duca was instead found guilty of an alternative charge of statutory murder - the unintentional killing of a person in furtherance of another crime, still deemed murder because of the circumstances.

Dr Alexander said Duca wasn't a man with a long history of violence.

"This offence most likely would not have occurred but for the drug use," he said.

He said rehabilitation was about a return to a crime-free life. While a return to drugs lowered that prospect, Duca's conviction on a most serious offence, his likely lengthy time in jail and abstinence from drugs while there, must be considered.

Dr Alexander provided character references from Duca's family and a psychologist report about his involvement with drug and alcohol counselling in custody.

Justice Lesley Taylor will sentence Duca at a later date.

Australian Associated Press