A "monster" who shot his son and his son's girlfriend, pausing to reload between the killings as the young woman took refuge in a bathroom and frantically called for help, has finally apologised for murderous behaviour.
Pawel Klosowski came before the South Australian Supreme Court for sentencing submissions on Monday and 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 killed them. I destroyed the lives of their families," he said.
"I acted like a monster. The world would be a better place if I had shot myself instead."
But prosecutor Kos Lessess said the apology was "too little, too late" and that the fact that almost the entire public gallery left the court, not wanting to hear what he had to say, "speaks volumes".
Mr 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."
The court heard that Lukasz was shot first and then Klosowski had reloaded his gun before firing once at Ms Ireland through the locked bathroom door where she had hidden and had rung triple zero.
A second shot, delivered at close range, had killed her.
Mr Lesses said there was no doubt Klosowski had intended to kill both his victims and described their deaths as towards the top of the range for murder offences.
In one of 22 victim impact statements presented to the court, Ms Ireland's father Greg said her death had stolen his best friend from him and shattered his heart, with the last moments of her life haunting him the most.
"They had nowhere to hide and nowhere to escape," he said
"Her last moments, knowing she was about to be shot, must have been horrendous beyond imagination."
Ms Ireland's mother Debra told the court that her daughter would have been so scared at that moment and that the "imagery of her final minutes haunts me".
"I feel so fragile, so broken, like I'm constantly teetering on the edge," she said.
"I feel like I'm living in some horror story."
Lukasz Klosowski's mother, Magda Pearce, described the killings as an act of "twisted evil" and told Klosowski he would "forever be remembered a murderer".
"Only you know what evil has perverted your soul to become the shadow of the man that stands before this court today," Ms Pearce said.
Because of his early guilty pleas, Klosowski is entitled to up to a 40 per cent discount on his non-parole period but Mr Lesses asked for any discount 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," Mr Vadasz said.
Justice Anne Bampton will hand down her sentence in April.