A Perth teenager has avoided a life jail term for murdering a stranger who was trying to help a 10-year-old boy recover a bike that had been stolen from him, and instead been sentenced to a term of eight-and-a-half years in juvenile detention. 

The teenager was 15 in May last year when he used an 18-centimetre filleting knife to fatally stab 42-year-old Petr Levkovskiy on a Sunday morning in the southern Perth suburb of Bull Creek.

Mr Levkovkskiy and his wife had been following the teenager in their car after hearing the cries of the 10-year-old whose mountain bike had been stolen by the teen.

When the couple caught up with him, Mr Levkovskiy put his arms around the teenager who, in an attempt to get away, pulled the knife from his pants and in a swinging, motion stabbed Mr Levkovksiy in the abdomen.

Mr Levkovskiy immediately collapsed on the driveway of a nearby house and was pronounced dead later in hospital.

Stabbing 'not intentional'

The teenager, who cannot be identified, was arrested the next day and charged with murdering Mr Levkovskiy.

While he accepted responsibility for his death, he maintained the stabbing was not intentional or deliberate and he should be convicted of the less serious offence of manslaughter.

After a nine-day trial, the jury deliberated for about seven hours before finding him guilty of the murder count.

Justice Anthony Derrick described as "fateful and unjustifiable" the teenager's decision to use the knife during his struggle with Mr Levkovskiy, saying he was satisfied the teen had intended to stab the 42-year-old in the area of the abdomen or torso, to try to get away.

In submissions in the Supreme Court this morning, prosecutor Clare Cullen said the state was not calling for the for the teenager, who is now 16, to receive a sentence of life imprisonment.

However, Ms Cullen argued for a significant term to be imposed, describing the stabbing as “a deliberate act” and saying afterwards, when he hid in bushes before fleeing to a friend’s house, the teenager showed a "callous attitude” to what he had done.

The 'disaster waiting to happen'

That included the friend filming himself asking the teenager how he “killed today” before getting the reply “I stabbed”, with the teen then demonstrating what he did.

The CCTV security cameras installed at the friend's home also recorded the teenager singing a song with the lyrics "I'm a murderer", which the court heard was a reference to a video on TikTok. 

Ms Cullen said at the time the teenager “was going down the path of idealising the gangster type of life” and he would carry a knife that she said he was prepared to use.

“This was a disaster waiting to happen,” Ms Cullen submitted.

She highlighted the teenager’s previous record, which included a conviction for assaulting a police officer by hitting him with a bottle.

Widow 'very disappointed' with sentence

WA Police Detective Senior Sergeant Keith Neubronner said Mr Levkovskiy's widow Anna was disappointed with the sentence.

"The sentence ... in her mind, obviously it's not sufficient, so she's extremely disappointed," he said outside court.

"At this point in time she can't bring herself to speak to anybody.

"Her words [were], 'I'm very disappointed'.

"It was a terrible case, it was a good Samaritan who was trying to do the right thing.

"Unfortunately the incident has turned out the way [it did] and he dies so it's terrible."

When asked whether there would be an appeal, he said that was a matter for the Director of Public Prosecutions. 

Banksia Hill conditions 'mitigating'

The teenager’s conduct in the notorious Banksia Hill juvenile detention centre was also detailed — the court heard it included him on one occasion climbing onto a roof during what was described as “unrest” at the facility.

The teenager’s barrister Simon Freitag S.C. said his client’s role in that incident was “as a follower”, and since then he had been working towards being transferred to a self-care unit where he would have a higher degree of independence.

Mr Freitag highlighted the current problems at the facility, including the repeated lockdowns, saying they should be taken into consideration in any sentence the teenager is given.

He also emphasised that at the time of the stabbing his client was only 15 years old and using drugs and alcohol, but Mr Freitag said during his time in detention he come to understand what he had done.

“We say he is not without hope,” Mr Freitag told the court.

The teenager had written a letter of apology which was tendered to the judge along with a booklet, from June last year, which the court heard was a collection of thoughts about his offence and the victim.

Justice Derrick said in the hours after the stabbing had boasted about what he had done, including singing the Tik Tok song about being a murderer, which he described as "immature" "thoughtless" and "callous."

Justice Derrick read aloud parts of the victim impact statements of Mr Levkovskiy's family, saying he wanted to make sure the teen "was in no doubt" about the impact of what he had done.

They included statements from his wife, Anna, in which she said she had lost "the love of her life" and her "soul".

Justice Derrick accepted that over time, the teenager had become genuinely remorseful.

He said in the booklet provided to the court, the boy had expressed shame and sorrow and in his apology letter to the court, he said he felt terrible for the pain he had caused.

The conditions at Banksia Hill were also regarded by the judge as a mitigating factor because of the lengthy lockdowns at the facility, when the teen was confined to his cell, as making his time in detention "more arduous".

The teenager will have to serve five-and-a-half years before he is eligible for release.