Pawel Klosowski faced the South Australian Supreme Court where Justice Anne Bampton said the “anguish and heart wrenching pain” he had caused for the families involved was profound.

“Your conduct was deliberate and purposeful,” she told him.

In recent submissions, Klosowski admitted he could not explain his actions at his rural property in the state’s southeast in August last year.

The 46-year-old had earlier pleaded guilty to the murders of his son Lukasz Klosowski and Chelsea Ireland, both aged 19, after an argument fuelled by alcohol and anger.

In a short apology read to the court he said he thought about what he had done every day.

“I acted like a monster. The world would be a better place if I had shot myself instead,” he said.

But prosecutor Kos Lesses said the apology was “too little, too late”.

Lesses said the shootings followed a row between Klosowski and his son after the teenager had indicated his intention to move out of his mother’s house.

“The offending came about due to the insulting of the defendant’s pride,” the prosecutor said.

“And it was fuelled by the combination of two fatal causes, anger and alcohol.”

Justice Brampton detailed how the argument had escalated with the killer berating his son at one stage for crying like a “little baby”.

She said affronted by perceived disrespect from his son and Ms Ireland, Klosowski’s behaviour escalated becoming irrational, reactive and ultimately violent.

The court heard that Lukasz was shot first in a bedroom and then Klosowski reloaded his gun before firing at the locked bathroom door where Ireland had hidden and called triple zero.

A second shot, delivered at close range, had killed her with her body found in the bath.

Because of his early guilty pleas, Klosowski was entitled to up to a 40 per cent discount on his non-parole period but Mr Lesses asked for any reduction to be significantly curtailed.

Defence counsel Nick Vadasz told the court that while Klosowski could not explain his actions on the night he accepted that his intention was to kill.

“The prisoner accepts the horror of his behaviour,” Vadasz said.

Justice Bamptom imposed the mandatory head sentence of life in jail with a non-parole period of 34 years.

Outside the court, Greg Ireland, the father of Chelsea, said both families would “never understand how this happened”.

“Today marks the end of one incredibly difficult chapter and tomorrow we continue the much more difficult task of learning to live without Chelsea and Lukasz,” he said.

“They were just beautiful, beautiful kids.

“We’ve all got life sentences, but we’re thinking this will probably be a life sentence for him as well.”

The mother of Lukasz, Magda Pearce, said the teenagers were “so good together”.

“We just want them back. They should be here,” she said.

-with AAP