Raelene Polymiadis, 65, is on trial in the South Australian Supreme Court charged with murdering Brenda and Lynton Anderson, who were both aged 94 when they died in March 2022 and May 2023 respectively.
Prosecutor Michael Foundas said a police listening device recorded her alone in her car praying to God on two separate occasions confessing to God that she had killed her parents.
"Please, Lord, you know, yes, I have sinned. I have. Thou shall not kill," she allegedly says in the recordings.
"I have sinned twice in my life, and I hate it, but I also know … your blessing, Lord, that they did not want to go to a nursing home, that was their wish."
The June 20, 2023 recording was made on the same day Polymiadis was interviewed by Major Crime detectives.
It also captured her praying to God for strength to show emotion where needed and to stop herself "with a tongue from running off at the mouth", Mr Foundas said.
A search of Polymiadis' house and car uncovered a set of notes written by her regarding what she should say to police when they spoke to her, the prosecutor said.
"It reveals that what she told police in that interview was planned and curated," he said.
"Ms Polymiadis has written to herself 'sob here', and that corresponds with a point in the interview where (she) commences sobbing.
"(It was) a clearly contrived account, including contrived emotions."
Polymiadis' denials to police lacked credibility and could be discarded, he said.
During the recordings, Polymiadis also "speaks in tongues", a phenomenon known as glossolalia, the prosecutor said.
A linguistics expert would give evidence that the recordings captured glossolalia, describing it as not some language other than English that changes the meaning of the English words spoken, he said.
Mrs Anderson died from an insulin overdose at the Flinders Medical Centre.
Mr Anderson died after he was found unconscious on his kitchen floor with a large amount of insulin within his body.
Polymiadis, a type 1 diabetic with access to insulin, had been the last family member to see each parent before they became unwell, Mr Foundas said.
He told the 14-person jury that one potential motive was a misplaced idea that killing her parents would spare them from going into a residential care facility.Both had expressed their clear preference against going into a nursing home and the prospects of that situation were looming large.
Defence counsel Marie Shaw KC said context and interpretation were issues with the alleged confession.
She said in the same prayer, Polymiadis says: "God, they've got into my stuff, and it's all my fault, they said it happens all the time with old people not wanting to go into nursing homes".
"Was my client admitting she was responsible for this, or was she telling her God that she felt responsible for their deaths?" Ms Shaw said.
"Because if they died of insulin administration, they must have accessed her insulin."
The trial continues.
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