Damien Russell Janson, 32, was motivated by anger after a failed drug transaction when he killed a friend of the drug dealer 23-year-old Jake Smith.

Mr Smith's mother said to the court in a victim impact statement her son was 'murdered for no reason' and she struggled with the loss of two of her sons.

Another son had died in a motorcycle accident years earlier.

"My life feels worthless, empty and sad. I feel powerlessness, hopelessness and worthlessness," she said.

"Jake's life was taken and so was part of me."

Jake's father said: "the cowardly and despicable way my son Jake was taken will haunt every hour and minute for the rest of my life".

Janson appeared at the Supreme Court of Victoria on Tuesday for a plea hearing, with his own family and the victim's family in attendance.

Crown prosecutor John Dickie said Janson's decision to grab the steering wheel while his friend was driving and veer the car to kill Mr Smith was 'voluntary', 'conscious' and 'deliberate'.

"He would have realised he was exposing Mr Smith to risk of serious injury or death," he said.

Mr Dickie said the offending was aggravated because Janson involved an innocent person in committing his crime and left him to deal with the consequences.

It was May 20, 2020 when friends met at Mr Smith's Werribee home and one friend asked if they wanted to travel to Bacchus Marsh with him to meet Janson.

The friend had arranged to sell drugs to Janson, who he had met in prison, but was annoyed so decided to give him a bag of kitty litter instead.

Mr Smith and another friend went along for the ride to Bacchus Marsh on their motorcycles with the friend in his car with two others.

Mr Dickie said Mr Smith did not know about the drug deal.

They parked at a 7-Eleven in Bacchus Marsh where the friend had arranged to meet Janson and Smith and the other friend on the motorbike and kept their distance from the car.

Meanwhile, Janson had been at his Pentland Hills home with his family when a friend came over to catch up.

Janson, who did not have a drivers' licence, asked his friend to drive himself and his brother to the service station so he could purchase drugs.

Janson arrived at 7-Eleven and got into the dealer's car with the intention to purchase drugs but both became agitated. He gave the man $50 to use to put the drugs on his scale.

The man pulled out of the service station with Janson still in the car and they continued to argue about the drug sale.

Janson's friend and brother followed in another car and Mr Smith and the other man on the motorbikes drove off.

Janson pulled out a screwdriver and the dealer pulled out a knife before he parked and Janson got out of the car.

Janson was picked up by his friend and brother and told his friend to follow the dealer's car as the guy had 'ripped him off $50'.

The dealer met up with Mr Smith and his other friend on the motorbike and they arranged to drive back to Werribee.

Both Janson in his friend's vehicle and the dealer with his friends were driving on Woolpack Road in Maddingley just after 7pm in opposite directions, back to Pentland Hills and Werribee.

Janson's vehicle passed the drug dealer's vehicle on the road and he recognised it and saw the two motorcycles, the first with Mr Smith, following behind.

Janson reached over from the front passenger seat and grabbed the steering wheel while his friend was driving and pushed it to the right.

It caused the ute to veer onto the wrong side of the road and collide with Mr Smith and his motorbike.

The motorbike rider behind saw Mr Smith thrown 20 metres over the top of the ute into a culvert off the road and the ute continued to drive away.

He called emergency services and a passerby gave Mr Smith CPR but he could not be revived.

The court heard Janson told his friend to keep driving but the friend stopped the car.

Janson ran off into paddocks while an air ambulance was called for Mr Smith and his friend and brother were left distressed in the car.

Police attempted to find him but he attended Bacchus Marsh Police Station by interview two days later.

He has been in custody almost a year since he was arrested.

Mr Dickie said Janson admitted to his psychologist he was under the influence of drugs at the time of the offending.

Defence barrister Dr Theo Alexander said Janson was 'truly and deeply remorseful' for 'what occurred on this day in a span of about two seconds'.

"The decision was made under the influence of drugs, with a lack of sleep and an impulsive character," he said.

Justice Elizabeth Hollingworth said a report prepared for court in 2018 had shown Janson needed treatment to address drug and emotional issues, but he had made no progress since.

The court heard he was on a community corrections order at the time of the offending.

"He has taken no responsibility to address his issues," Justice Hollingworth said.

Dr Alexander said this offending would have a lasting effect on Janson and he had reasonable prospects for rehabilitation.

"I urge the court to take the view this was a split second decision in the fog of drug use," he said.

Justice Hollingworth said Janson's moral culpability was high because he was looking for the dealer and his friends after the transaction failed.

She scoffed at Dr Alexander's description of Janson as a person of good character.

"He has for years thumbed his nose at the law. He has a very lengthy criminal history," she said.

"I don't understand how you can describe him as a person of good character.

"He has priors for recklessly causing injury and criminal damage. Unless something is done to address his use of drugs, this is the type of offending that can happen.

"He clearly has a history of impulsive behaviour in a vehicle and a vehicle can be a lethal weapon. Where can I get the comfort that this is not going to happen again?"

In prosecution submissions, Mr Dickie said it must have been terrifying for Mr Smith to see the ute swerve into his path.

"My submission is the culpability is high and the offending constitutes a serious example of a serious offence of manslaughter," he said.

The court heard Janson had served a period of imprisonment in the past.

Mr Dickie said specific and general deterrence, protection of the community, denunciation and just punishment were significant principles in sentencing.

The maximum penalty for manslaughter was raised from 20 years to 25 years' imprisonment last year.

Janson will return to court at a later date for sentencing.

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