Within an hour of leaving Wishhasad Somawansa's Hoppers Crossing home on February 18, Baea returned and murdered his schoolfriend's mother, Prasad, by stabbing her at least 38 times in the head, neck, chest and arms with a knife he had with him.

Baea, 22, had earlier that night eaten dinner with Mrs Somwansa, 48, and her son after arriving at their home unannounced, having run into his former school friend about a week earlier, when the two young men agreed to catch up some time.

After dinner, Mr Somawansa was paged by his SES unit and drove Baea to a shopping centre.

But, prosecutor Sharn Coombes told the Supreme Court on Wednesday that CCTV cameras caught Baea turn around at the shopping centre and walk back towards the Somawansa home.

He later told police he thought he had left his Myki card behind and when he returned, and was told to "piss off" by Mrs Somawansa.

"I got angry about that and I, I stabbed her," he told police. He acknowledged he "gets angry easily".

Ms Coombes said Baea told police he only stopped stabbing Mrs Somawansa when she fell, and did not help her because "she was dead or something".

Defence counsel Ruth Shann said her client killed out of anger, but there was no real explanation for why he targeted "someone who was a virtual stranger to him".

Ms Shann described Baea's reconnection with Mr Somawansa as a "sliding doors moment", as they were together at primary school in Tarneit but went different ways afterwards.

After he left primary school, Baea's family returned to their native Papua New Guinea, where the boy and his younger sister were abandoned by both parents.

Baea returned to Australia last year to visit his mother, the court heard, but learned she had no intention of having her son and daughter stay permanently. He was due to return to Port Moresby on February 21.

"To spend the day with his old friend and then find himself in a house with two loving parents supporting a son who was studying was very confronting," Ms Shann said of Baea's visit to the Somawansa home.

"He felt jealous of that love." Mrs Somawansa was on the telephone when Baea returned, Ms Sharn said, and told her friend she would ring back in five minutes. She never did.

But during the attack, husband Priyantha Hewage, an interstate truck driver who was in Brisbane working, rang and realised his wife was in trouble when she somehow answered the phone.

Mr Hewage told police he heard his wife say "You go out, you go out, you go out" and then call "Dos, Dos, Dos", the name she called her husband of 22 years.

Mr Hewage rang a workmate to attend his home, and the colleague found Mrs Somawansa. She could not be revived.

Mr Somawansa, his father and his girlfriend were in court on Wednesday, often with their heads bowed after Baea formally pleaded guilty to murder.

Ms Shann said Baea developed anger issues during his teenage years, after his mother went back to Australia and his father began a relationship with another woman.

Baea had never been equipped with the tools to control his anger, his lawyer said, and spoke about wanting to assault his father to Mr Somawansa that night.

But there was good in Baea, Ms Shann said, given the responsibility he took in caring for his sister amid the violence in Port Moresby.

He was now racked with guilt and socially and culturally isolated in custody, having cut himself off with any contact he had with his family.

Justice James Elliott will sentence at a later date.