Clifford Arthur Neumann, 41, of Morphett Vale, stared at the floor as he was handed a minimum prison term of almost 23 years in the SA Supreme Court on Wednesday for the murder of Victoria Stewart, 39.
Ms Stewart was one of four women found dead in unrelated incidents across South Australia in a single week in November 2023, prompting the state government to order a royal commission into family, domestic and sexual domestic violence.
Neumann and Ms Stewart had met about 15 years ago when they were members of the same Jehovah's Witness congregation, and reconnected via Facebook in August 2023, Justice Laura Stein said.
He later told forensic psychologist Loraine Lim that he had hoped Ms Stewart would leave her partner to be with him.
"However ... you became increasingly suspicious that Ms Stewart was hiding things from you and was still in a relationship with (her partner)," Justice Stein said.
Dr Lim found there was likely to be a "direct nexus" between his "mild to medium level" autism, and developing an obsessive plan to kill Ms Stewart, Justice Stein said.
"Dr Lim considered your restricted capacity for perspective-taking and empathy, as well as poor inherent understanding of human emotions and behaviours and an inability to appreciate social cues, most probably caused you to grossly misinterpret the changes in Ms Stewart's behaviour," she said.
When Ms Stewart visited his home on November 19, he enacted a "clearly premeditated" plan to kill her with a steel bar.
"For the sake of Ms Stewart's family members ... I will not describe what you told police you did to Ms Stewart, or the details of the pathology report or the scene that police later observed in the lounge room," Justice Stein said.
"The evidence establishes that you attacked Ms Stewart with ferocity ... (it) was brutal and frenzied, and blows were delivered with terrible force."
"You carried out the attack on a defenceless woman who could do nothing to fend you off."
The judge said Neumann went to Victoria Stewart's home with a clearly premeditated plan to kill her. (Supplied/AAP PHOTOS)
After being "wracked with guilt and grief" for Ms Stewart and her children, Neumann contacted police and told them he had done "a horrible thing" and was sorry.
Neumann's autism diagnosis was relevant but did not significantly reduce his moral culpability or moderate the need for denunciation or deterrence, Justice Stein said.
"You knew you were planning to do a bad and horrible thing, you knew the consequences," she said.
The judge accepted Dr Lim's assessment that Neumann had prospects for rehabilitation, including his insight into the unforgivable impact of his conduct, his guilty plea, his generally non-confrontational personality, lack of any traits of antisocial personality disorder, and intelligence.
The judge acknowledged the "extremely moving" victim impact statements from Ms Stewart's mother, brother, sister, daughters, partner and former husband.
"They spoke of their deep grief, anguish and bewilderment at your actions," she said.
"Your actions have inflicted an unimaginable, profound suffering which I cannot adequately capture in a few short sentences."
Justice Stein said the murder of a person in a relationship context was "abhorrent and deserving of the greatest level of denunciation".
The judge acknowledged deep grief, anguish and bewilderment expressed in family's impact statements. (Morgan Sette/AAP PHOTOS)
With a 15 per cent sentence discount for his early guilty plea, Neumann's 27-year non-parole period was reduced to 22 years, 11 months and 13 days.
Outside court, Ms Stewart's brother, Douglas Jones, said the family was "pretty happy" with the sentence.
"I appreciate the judge took everything into consideration, it felt like a little bit of justice in a pretty poor situation.
He said his sister was "the best of us".
"She was caring, loved her kids. I am very proud of who she was. I just miss her," he said.
Ms Stewart's daughter, Tara Songer, said the jail term was "never going to be enough".
"No matter how high or low, the pain and suffering that me, my siblings, my family, my mother's friends ... have all encountered, it was never going to be enough to justify that pain," she said.
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