Psychological reports show Hillier triple murderer Steven Graham Peet was planning to kill one of his victims before her death

THE Hillier triple murderer told a fellow prisoner he had already planned to kill his lover before his crime — and would have also killed two Families SA workers if they intervened.

Victims Korey Lee Mitchell and his sister Amber Rose Rigney.

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THE Hillier triple murderer told a fellow prisoner he had already planned to kill his lover before his crime — and would have also killed two Families SA workers if they intervened.

Psychological reports released by the Supreme Court on Monday show how Steven Graham Peet’s claim of a “disassociative state” — which derailed his trial for five months — fell apart.

In his report, Dr William Brereton says the method by which Peet fatally bound and gagged Amber Rose Rigney, 6, and Korey Lee Mitchell, 5, was “incompatible” with his claim.

“By his own account, Peet hid their mother’s body, went out for a smoke, made the children breakfast and formulated a plan to take them to their father, which he told them about,” he said.

“He trussed them up in a complicated manner ... it’s not credible for Peet to assert he did not know his actions would almost certainly result in the deaths of the children.

“He was worried about the discovery of his offence ... his actions were a complex and protracted series of actions to achieve a clear goal — avoid discovery.”

Steven Graham Peet following his arrest. Picture: Emma Brasier

Peet, 31, murdered the children and their mother, Adeline Yvette Wilson-Rigney, 28, at their Hillier home on May 30, 2016.

All three died around the time two Families SA workers knocked on the door of the house.

Peet’s claim of having been in a “disassociative state” when the children died arose from the August 2017 report of forensic psychologist Luke Broomhall.

Mr Broomhall said Peet’s “patchy recall” of events was likely caused by the abuse he had suffered during his relationship with Ms Wilson-Rigney.

In his November 2017 report, Dr Brereton disagrees — and points to Peet’s conduct in prison.

“In March 2017, Peet told (another prisoner) he had organised to borrow a gun from a friend and arranged to kill Yvette on the Tuesday, the day after she was actually killed,” he said.

“He said (on the day of the murder) Amber became suspicious ... Families SA knocked ... Peet told the children to be quiet and go into their bedrooms.

“He said he separated the children as he thought he may have to kill them, (and) if the Families SA workers had entered the house he would have killed them, too.”

Adeline Yvette Rigney-Wilson with her children Korey Lee Mitchell and Amber Rose Rigney.

Dr Brereton said that, during his assessment, Peet insisted he did not mean to murder the children.

“He said ‘I thought they’d be all right ... they were beautiful kids, I didn’t want them to die, they didn’t deserve it,” he said.

“He said ‘I want my side told, people can judge me all they want ... I’m not a monster, I did not intend to do it.”

Peet will be sentenced on a date to be set.

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