Justin Stein, 34, has pleaded not guilty to murdering nine-year-old Charlise in January 2022 as he stands trial in the NSW Supreme Court.

Charlise’s body was found dumped in a barrel by the Colo River, northwest of Sydney, four days after she was reported missing by her mother Kallista Mutten.

Giving evidence as the defence case began on Monday, Stein told the court he witnessed Ms Mutten shoot her own daughter, and afterwards told him to lie to police.

At the time Ms Mutten was in a relationship with Stein, and the pair had discussed plans to get married, the court heard.

Stein told the court on the night of January 12, 2022, he had been working on his car in a shed when he heard a gunshot and Charlise call his name.

“I went outside the shed … that’s when I heard Charlise screaming, ‘mummy, no’, and then bang, there was a second gunshot,” Stein said.

I said, “what the f*** have you done,” Stein told the court.

Stein said Ms Mutten repeatedly screamed at him, “you did this” and pointed the weapon at him, telling him to get a tarp from the shed.

When he returned from getting a tarp, Stein said both Ms Mutten and Charlise were gone.

Stein said he returned to the house where he rolled a joint in an attempt to calm himself down.

“I eventually stopped crying, I smoked that joint,” Stein said.

Stein said he didn’t see Ms Mutten again until the next day, when she left the property in his car, prompting him to report the vehicle as stolen to police.

Despite two officers attending the property that day, Stein didn’t tell them anything about what he claims had happened to Charlise.

“Why didn’t you, at that stage, tell the police what you’d seen happen the night before?” Stein’s lawyer Carolyn Davenport SC asked him.

“I honestly don’t know. I’ve asked myself that question a lot and I don’t know why I didn’t do it,” Stein replied.

“I just couldn’t get myself to speak.”At the time of her death, Charlise was visiting her mother and Stein for a month from Queensland where she lived with her grandparents, who had legal custody over her.

During the visit, the group spent their time between a Mount Wilson property owned by Stein’s mother and a caravan at the Riviera Ski Park, about a 90-minute drive away.

Stein said during the visit Ms Mutten had become jealous of the bond between him and the schoolgirl.

“We got along really well. (Charlise) was always next to me, always wanting to hold my hand, always wanting to be with me,” he said.

The night before her death, Stein told the court he returned to the Mount Wilson Property alone with Charlise.

“Charlise told me she didn’t want to stay with Kallista and she asked if she could come back with me,” he said.

Stein said during her stay at Mount Wilson, Charlise slept in her own bedroom at the property but would not always remain in her room all night.

“She was in my bedroom when I went to bed,” Stein said.

The next day, Stein says Charlise was unwell, but didn’t want to be left alone and travelled with him and Ms Mutten to Sydney in the back of his ute where he put her with garbage bags, a blanket and a small pillow.

Prosecutors allege Charlise was not in the car at that time, which was also the evidence given by Ms Mutten.

Stein told the court he had started taking heroin at the age of 12 and was diagnosed with schizophrenia at 21, which gave him periodic auditory and visual hallucinations.

To treat his schizophrenia, Stein was prescribed the anti-psychotic medication quetiapine, also sold under the brand name Seroquel.

“It makes me able to function. It stops the voices, not completely, but it does stop them,” Stein said.