Wendy's brother killed their parents over a $40 bottle of wine. Then he fought for their inheritance.

It was 10pm on a Wednesday night, in December 2014, when Wendy Robinson woke to the doorbell ringing incessantly.

She thought she was dreaming at first, but when it didn’t stop she stirred awake and noticed a cop car outside the window.

“Please don’t tell me it’s my children,” she asked the officer after racing to the front door. “No it’s Ian and Marg,” she was told.

She knew immediately who was responsible.

“What’s Scott done?” she asked, and the reply confirmed her worst fears: “he’s shot them.”

“It was the weirdest feeling, it was like the room closed in around me. I remember it going all blurry,” Wendy told Mamamia.

Her brother, seven years her junior, had shot and killed their parents, Ian and Margaret Settree, inside their family home in Cobar, NSW.

WATCH: Wendy will be on this week’s SBS Insight on Unthinkable Acts. Post continues after video. 

Since the age of 15, Scott Settree had seemingly hated his family.

But Wendy remembers a wonderful life, with “amazing holidays”.

Their parents, married 53 years, were hopelessly in love until the day they died and worked tirelessly to give their family everything.

But Scott blamed them for everything that went wrong in his life. As he grew up he started drinking, getting into drugs, and then entered an abusive relationship.

Wendy describes a gradual escalation of his violence and narcissistic tendencies until eventually, in his 30s, he started having delusions.

As an adult, Scott moved back in with his parents after his relationship broke down, and very quickly took over his parent’s home. In 2014, he was 46, unemployed, and spent most of his time drinking and ordering his parents around.

Wendy says her father confided in her that he "felt like a prisoner in his own home". But her mother's love was unconditional, and she would stick up for Scott no matter what.

"As we saw him get more and more violent, my children and I feared something was going to happen. I never thought he would kill them, but I thought he would badly hurt them," Wendy told Mamamia.

The night of the double murder, Ian snapped. He couldn't take it anymore.

He asked his son to reimburse him for the $40 bottle of wine he'd drunk of theirs without permission. Within hours of that altercation, Scott took the loaded shotgun he secretly kept underneath his bed and fatally shot both of his parents.

"We were allowed to watch his video interview [from that night] once the trial was over. As a family we watched him say he'd had enough of mum and dad, and now he 'feels free'. He took pleasure in telling the story. It was sickening," Wendy explained.

"He described their deaths in so much detail that I was nearly vomiting, it was horrible."

Despite the videotaped admission and a signed admissions statement, Scott was found not guilty by reason of mental illness, after being diagnosed with paranoid schizophrenia within the prison system.

While the judge ordered an indefinite incarceration, his sentence under the Mental Health Act means he holds no criminal record.

It also meant he was entitled to half of his parent's estate, which was around one million dollars.

"There was no way he was getting anything of mum and dad's after killing them. It wasn't about the money, it was about the principle," Wendy told Mamamia.

She filed a case to have her brother forfeit his half of their parent's money. But as the case went to court, Wendy was dealt another blow. Ian's younger sister - her aunt - had been visiting Scott behind bars to become his power of attorney, so she could fight Wendy on his behalf.

"She was helping the killer of her brother. I was so upset, I was an emotional mess. Her doing that was like another death in the family. It divided the family."

Eventually, Wendy won the case. But there were conditions. She was ordered by the judge to pay her brother $100,000 for "his well being" and cover both of their legal costs. The defence invoice came in at $150,000.

Wendy was left broken.

It's been more than five years since her parents were killed. She misses them terribly, and hasn't spoken to her brother since he waltzed into the family business on the morning of the murders, grumbling to her about the fact she wasn't spending Christmas in town.

"I'm not having Christmas by myself with f***ing mum and dad," she remembers him complaining.

"I hate him. I feel so much anger. My children tell me it's a waste of energy to feel like that. But I do."

Right now, Wendy's fighting to change the laws that led to her brother's sentence. She would like to see mentally ill offenders held responsible for their crimes.

"I want the words 'not guilty' changed. He is guilty of what he did, he signed a statement saying his intentions were to kill mum and kill dad."

Wendy is devastated that those sentenced under the Mental Health Act don't have a criminal record, explaining that if her brother one day manages to get out, he's "as clean as a whistle".

The NSW Government has confirmed it plans to replace the special verdict later this year, with the state's Attorney General Mark Speakman telling SBS: "For victims and survivors, criminal proceedings can be a distressing and potentially traumatising experience. This can be exacerbated by hearing that a mentally ill person is ‘not guilty’ of an offence, even though the court found the defendant committed the act."

Wendy still lives in Cobar, where every corner of the small town reminds her of her parents. She'd spent every day working alongside them in the family business, and sometimes she'd pop around to see them after dinner for a cup of tea before bed.

"I am lonely for family," she told Mamamia. 

"As a victim, your own mental health starts to deteriorate. There are many different emotions. Sometimes I have meltdowns. But somehow you become a little bit stronger. You don't get over it, but you live with moving forward," she said.

Feature image: Supplied. 

You can hear more from Wendy on SBS Insight tonight at 8.30pm.