An inquest has heard a father who killed his baby daughter at the Whispering Wall spoke about taking her to the site one month before the murder-suicide.

WARNING: This story contains details that readers may find distressing.

Nine-month-old Kobi Shepherdson was killed when her father, 38-year-old Henry Shepherdson, took her to the Barossa Valley tourist attraction in April 2021.

A coronial inquest is currently investigating the circumstances surrounding their deaths, overseen by Deputy State Coroner Ian White.

On Friday, the inquest heard nine recorded phone calls made from Shepherdson while in custody in Mount Gambier Prison to Kobi's mother.

The calls were made between February and March — one month before Kobi's death.

Kobi's mother said she was going to take her daughter on a drive to the Barossa Valley, Shepherdson asked whether Kobi had been to the Whispering Wall.

"I want to go there with Kobi," Shepherdson said.

'Please don't do this'

Documents obtained by the ABC from the Coroners Court show that Shepherdson called Kobi's mother in the lead-up to the murder-suicide telling her "this is the way it has to be".

"I then called him back and that's when Henry told me he and Kobi would not be home when [I] got home," she said in a statement to police on May 19, 2021.

"I knew what this meant and I said 'please don't do this', I said 'she's just nine months old you can't do this'.

"I knew from a previous conversation; I asked him if he was at the Whispering Wall but he wouldn't answer me.

"I then said, 'Please don't do this, not my baby girl.'

"He just said 'this is the way it has to be' then he hung up."

Kobi's mother further said in her statement that if he ever thought of ending his life then he would go to the Whispering Wall.

"Henry told me not long after we first met, if he ever had thoughts of killing himself he would go to the Whispering Wall," she said in the statement.

"He wasn't suicidal at the time he told me but he said if he thought he had no other way out that's what he would do.

"I never thought Henry was ever capable of doing anything to his baby girl.

"When I left Kobi with Henry on that day I had no reason to believe Henry was planning to take his and Kobi's life."

Kobi's mother said Shepherdson had called her several times that afternoon and in the one before the last could "hear Kobi in the background".

"The call lasted about two to three minutes," she said.

"He didn't say which park he had gone to, I just assumed it was one near home."

'Extreme coercive behaviour'

The inquest was told how Shepherdson contacted Kobi's mother as many as 14 times a day from prison, repeatedly manipulating and pressuring her to go to the police and drop serious domestic violence charges against him.

The conversations were in breach of a non-contact order between the pair.

The deputy state coroner described the calls as examples of "extreme coercive behaviour".

Shepherdson told Kobi's mother to be "careful" when arranging to drop the charges, concerned it would appear she was being coerced and repeatedly asked her if she was feeling pressured.

"Do you want me home or not? … because it's all in your power," he said.

"This isn't me telling you to do this… I'm saying I heard this is the way we do this for us and for our family to come back together again."

Shepherdson said going to court would "drive a bigger wedge" between the pair and warned she would be pulled apart by defence lawyers.

"I'm going to think this was unnecessary … we could just find our own way around it."

After Kobi's mother missed incoming phone calls from the prison, Shepherdson told her he had a "right" to speak to her.

"Why do I have to ring 100 times before you answer, that's just not going to work for me," he said.

"I want to be able to see my daughter, if you're going to be playing these games, I don't want a bar of them."

The inquest before Mr White continues.