Justin Stein's mother has denied changing her story about a phone call on the day of schoolgirl Charlise Mutten's alleged murder to cover for her son.
Stein, 33 is accused of murdering nine-year-old Charlise and dumping her body in a barrel by the Colo River, northwest of Sydney, in January 2022.
His mother Annemie Stein told his NSW Supreme Court trial that she heard a "cheeky" voice in the background of a phone call on the evening of January 12.
During the phone call Stein told her he was with Charlise and her mother Kallista Mutten at a Mount Wilson property in the Blue Mountains, which was owned by Ms Stein, the court was told.
Ms Mutten previously told the court by that time she did not know where her daughter was, and had not seen her since the previous day when she allowed her to stay with Stein at the property alone.
Despite previously telling police she had not heard anyone else in the call, Ms Stein said during her evidence on Thursday she was certain she heard a voice, which she believed was Charlise, but could also have been Ms Mutten.
"What I'm suggesting to you is that your answer about hearing a voice in the background ... is something you have added to your evidence to assist your son," crown prosecutor Ken McKay SC said.
"I definitely heard a voice," Ms Stein said.
Stein and Ms Mutten had been in a relationship and discussed plans to get married, but Ms Stein told the court she was "not a fan" of her prospective daughter-in-law.
"My relationship with her was not good, period," Ms Stein said.
"Her erraticness, the ups and the downs, the way she was with her child, the aggression she showed her child.
"It wasn't a comfortable mother-daughter relationship, as it should be."
Ms Stein also told the court that her son was providing most of the care for Charlise during her visit from the Gold Coast, where she lived with her grandparents.
"She felt comfortable with Justin," Ms Stein said.
"It was lovely. It was a nice relationship."
Stein initially told police the last time he saw Charlise was when he left her in the care of a woman he believed to be a property valuer who arrived at the Mount Wilson property on January 12.
He said he believed the woman had been organised to come there by his mother.
But Ms Stein said she had no recollection of telling her son a valuer - who she had earlier engaged - would be coming back to the property during the week Charlise disappeared.
She said she arrived at the Mount Wilson property on January 14 to find it crawling with police, who told her it had been declared a crime scene.
Ms Stein told one of the officers of her son's claims about leaving Charlise with the property valuer in a conversation recorded on a body-worn camera.
"I said (to Justin), 'Did you get her name?'," she told the officer, according to a transcript of the recording.
The officer replied that he assumed Stein would have the valuer's full details because you "wouldn't let a nine-year-old go off with a stranger".
"That's what doesn't add up," Ms Stein replied.
Stein later admitted he lied about leaving Charlise with the woman, but he said Ms Mutten had been the one who came up with the story and told him to tell police.
Ms Mutten told the court earlier in the week that Stein had given her the same account of what happened to her daughter, before he also suggested Charlise may have been taken by former associates from his criminal past.
His lawyer Carolyn Davenport SC suggested he had witnessed Ms Mutten shoot her daughter and he had lied to police to protect her.
Ms Mutten denied those allegations during her stint in the witness box.
The trial continues on Friday.
