Slain schoolgirl Charlise Mutten probably spent her final moments in terror, a grim likelihood that justified a life sentence for her heartless murderer, a court has been told.
The nine-year-old longed to have a father, but the man she trusted to fill that role and called "Daddy" instead shot her dead and dumped her body inside a barrel.
A jury in June found Justin Stein guilty of Charlise's murder despite his claims the girl's mother Kallista Mutten, with whom he was in a relationship, was responsible for the shooting.
Justice Helen Wilson told a sentence hearing on Friday the girl's young age and the callous manner of her death were significant factors for her to consider.
Police located Charlise's body on January 18, 2022, near the Colo River northwest of Sydney, with close-range gunshot wounds to her face and lower back.
It was possible Stein had shot the girl once while she tried to flee before firing another shot directly into her head, Justice Wilson said.
"It's almost akin to an execution," she said.
Crown prosecutor Ken McKay SC told the NSW Supreme Court that based on the extreme nature of the crime, the only appropriate sentence for Stein was life in prison.
"Charlise Mutten must have been in great fear until the final fatal shot," he said.
Stein's lawyer Carolyn Davenport SC argued a non-parole period above 25 years would still be a significant portion of his life and he would likely spend much of his sentence in some form of isolated protective custody.
"It would be very cruel and unusual punishment to send a 33-year-old man to prison for the rest of his life," she said.
Charlise had been visiting her mother and Stein over Christmas from the Gold Coast, where she lived with her grandparents, at the time of the murder.
She spent the night of January 11 alone with Stein at a property at Mount Wilson, in the Blue Mountains, while her mother stayed at a caravan at the Riviera Ski Park, about a 90-minute drive away.
Ms Davenport argued Stein hadn't planned the murder in advance and noted Charlise had chosen to return to Mount Wilson alone with him.
"There was certainly no planning to have this child alone with him," she said.
"There was no motive that we know of. Something happened that sparked off a reaction by him."
In a victim impact statement, Ms Mutten said by placing her trust in Stein she had unknowingly put her daughter in harm's way.
"Charlise just longed for a dad," the distraught mother said.
"She trusted in my judgment and I just hate myself for being so wrong about it."
Charlise's grandfather Clinton Mutten, who was her primary carer, said the failure to protect the young girl would haunt his family for the rest of their lives.
"Her murder by a person of whom she trusted, was calling 'Daddy' and hoped for him to one day be a caring father for her, I believe breaches all sense of decency and trust," Mr Mutten told the court.
"Was Charlise hunted down, incapacitated and murdered, pleading for her life?
"These are questions that I believe will never be answered and will be a burden that I will carry for the rest of my life."
The same day Charlise's body was found, investigators arrested and charged Stein with her murder after using location data from his phone to pinpoint where the barrel was dropped.
Stein would later admit dumping the body, but he claimed he panicked after discovering it on the back of his ute.
Toxicology results revealed Charlise had traces in her body of the anti-psychotic drug Seroquel, for which Stein had a prescription to treat schizophrenia.
An adult dose of the drug would have a profound sedating effect on a child, the court heard.
Justice Wilson will deliver her sentence on Monday.
