Maximum term urged for SA triple killer

A judge has been urged to give the maximum possible sentence to Steven Graham Peet following his guilty pleas to murdering his partner and her two children.

Peet has admitted murdering Adeline Yvette Wilson-Rigney and her children Amber, six, and Korey, five, at their home north of Adelaide in May 2016.

He strangled all three with cable ties but also inflicted serious head injuries on Ms Wilson-Rigney.

In sentencing submissions on Wednesday, the children's grandfather Steven Egberts asked Justice Malcolm Blue to jail Peet for as long as possible, "because of the cruelty shown to Amber and Korey".

"I would ask for the maximum allowable sentence," Mr Egberts said.

Under SA law, Peet will receive a mandatory head sentence of life in jail, but the court can impose a non-parole or minimum period he must spend behind bars.

Mr Egberts said the deaths were an "incomprehensible tragedy".

"All of our family and friends have been impacted in their own cruel ways," he said.

"The impact this has had on me is something that can't be explained in such a short period of time.

"It will leave a hole in my heart forever."

The bodies of Ms Wilson-Rigney and the children were all found with cable ties around their necks and hidden under clothes and bedding and, in the case of the boy, under a child's play tent.

The young girl had adhesive tape wrapped around her head and a sock had been stuffed in her mouth.

Her arms had been tied behind her back.

The young boy had parts of his body wrapped in tape and his hands and feet were secured behind his back in a hog-tied fashion.

Ms Wilson-Rigney's head injuries were consistent with being struck with the claw-end of a crowbar or a hammer.

Her body was found in the laundry but evidence suggested she was attacked in another room and dragged there.

In earlier submissions, defence counsel Bill Boucaut said Peet would feel "shame and regret" for the rest of his life.

Prosecutor Tim Preston said Peet killed Ms Wilson-Rigney in anger and her children because they witnessed their mother's murder.

The two children were killed because they could implicate him in the murder of their mother, Mr Preston said.

Justice Blue will sentence Peet on a date to be fixed and will also rule on what material from the killer's psychological reports can be released.