Lachlan Young, 23, faced the Victorian Supreme Court in Ballarat on Wednesday for the start of his murder trial.
He has pleaded guilty to the lesser charge of manslaughter, admitting he did kill his former partner Hannah McGuire on April 5, 2024.
But he denies murdering the 23-year-old, claiming her death was instead an "unplanned and spontaneous" event.
Crown prosecutor Kristie Churchill told the jury his manslaughter plea was rejected, instead alleging Young formed a plan to murder Ms McGuire.
The prosecutor told the jury Young had been controlling and abusive towards Ms McGuire, and intervention orders were taken out against him.
After the second court order was made in March 2024, Young realised his relationship was over and he would lose the house they had bought together so he killed her, Ms Churchill claimed.
It's alleged Young told a workmate on April 2 that he would "roofie" Ms McGuire, drive her out somewhere and crash the car while she was unconscious.
Two days later, Ms McGuire went to their joint property about 9.47pm to meet with Young.
She never left the house and it's alleged Young murdered her sometime between 1.50am and 2.53am on April 5.
He then placed her body in the footwell of her Mitsubishi Triton, drove out to Scarsdale, about 25km south of Ballarat, and set fire to the car.
Young allegedly left the scene with his workmate as the getaway driver in a separate vehicle.
On the drive back, Young used Ms McGuire's mobile phone to send messages to her mother Debbie, claiming she was going to take her own life.
"I'm sorry Mum, I thought this was the right decision," text messages read to the jury stated.
"I tried to heal and cope with it all but I'm not OK."
Young also sent himself messages from Ms McGuire's phone, saying "I'm sorry, I love and miss you dearly".
The accused murderer also transferred $2000 from Ms McGuire's bank account to her mother and $5000 to himself.
When Ms McGuire's mother went to Young's house in a panic, he claimed he had not seen her daughter and feigned surprise at the messages.
Ms Churchill alleged they were some of the lies Young told Ms McGuire's parents, his own family, and the police.
After he was arrested on April 7, Young told officers he would "never f****** harm that girl".
Defence barrister Glenn Casement admitted Young had made "appalling and bad choices" to try to cover up what he had done.
But he told the jury that did not mean his client was guilty of murder.
The killing was instead an unplanned and spontaneous event that lacked murderous intent, Mr Casement said.
It was not disputed that Young sent the text messages from Ms McGuire's phone and made the bank transfers, the barrister said.
But the allegations made by Young's workmate were contested and Mr Casement urged the jury to be critical of the man's account when he gives evidence.
Jurors should also carefully assess Ms McGuire's decision to go to the house voluntarily before her death and the circumstances surrounding the intervention orders, Mr Casement said.
The trial before Justice James Elliott continues.
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