He also forced Ms O’Brien to eat an apple so she could be like Eve and be enlightened.
Sturt was taken to hospital but released that night.
“I would never hurt you,” he told Ms O’Brien in a text.
“I hope so. I get scared,” the woman replied.
“Of what?” he asked.
“Of you murdering me,” she said.
On June 25, Sturt went into the couple’s Gardenvale bedroom talking about the end of the world.
He started to pull Ms O’Brien’s pants off, saying he wanted to see if he was still attracted to her.
She fought back and armed herself with a pair of scissors but Sturt turned them against her.
He held a pillow over her face until she lost consciousness.
Sturt then tied a pair of tracksuit pants around Ms O’Brien’s neck to make sure she was dead.
He had a long history of violence towards his girlfriend before killing her amid a cannabis-induced psychotic state, the Supreme Court was told on Monday.
He pleaded guilty to murder in March.
After killing Ms O’Brien, Sturt showered, went into the city and approached police saying, “I just killed my girlfriend.”
“No you didn’t,” the officers replied before Ms O’Brien’s body was found on her bed.
Sturt has since been diagnosed with schizotypal personality disorder.
He told police “in that moment, it [the murder] felt like the right thing to do”.
“I know it sounds horrible,” he said.
“It just felt necessary at the time … like everything was leading up to that.”
He said Ms O’Brien was a psychopath and he confronted her that morning, saying: “You’ve been killing people.”
Sturt was profoundly remorseful for what he did, his Legal Aid lawyer Tim Marsh told the court.
He said Sturt was deeply affected when he read a statement by Ms O’Brien’s mother, who described losing part of her soul when her daughter died. The killer accepted he had lost the chance for a normal life and acknowledged it was the price he must pay.
Sturt has participated in numerous prison programs, including a drug and alcohol program, and was working in the laundry.
He remains in custody and will be sentenced at a later date.
If you or anyone you know needs support, you can contact the National Sexual Assault, Domestic and Family Violence Counselling Service on 1800RESPECT (1800 737 732), Lifeline 131 114, or beyondblue 1300 224 636, or the Victims of Crime Helpline 1800 819 817.