An ACT Supreme Court judgment, published late on Tuesday, shows Ashleigh Wayne Wilson was recently sentenced to four years and nine months behind bars over the attack.

Acting Justice Stephen Norrish ordered the 34-year-old Richardson man to serve a non-parole period of two years and four months.

Wilson's nephew, Andrew James Francis Beath-Williams, 24, was sentenced to two years and three months in jail over his role in the events leading up to the October 2020 stabbing.

The younger man received a non-parole period of 12 months.

Both offenders were initially charged with attempted murder after they lured the victim, whom they suspected of sexual abusing someone they knew, to a car park in Gowrie.

The victim went there with his mother, believing they were meeting a cannabis dealer.

He was instead "ambushed" and stabbed by both Wilson and another man, who has not been charged because police have been unable to find him.

Acting Justice Norrish said Wilson had got into a car with the victim and knifed him in the neck.

The 34-year-old and the other armed assailant also stole the victim's watch and $110 in cash.

While Beath-Williams drove his co-offenders to the scene of the incident, and knew they had knives, he did not take part in the attack or know there was going to be a stabbing.

Acting Justice Norrish said independent evidence showed the 24-year-old had been "very concerned" upon discovering what had unfolded.

He said Beath-Williams had, on the night of the incident, told someone: "Oh f---, it went wrong. It was just meant to be a bashing. [The victim] got stabbed."

The judge also noted that there was no evidence the victim had in fact committed the sexual offence the attackers had suspected him of.

Acting Justice Norrish denounced the "vigilantism" involved in the incident.

"People are not entitled, no matter how grievously affected they believe other third parties may be, to take the law into their own hands," he said.

"It usually ends badly, as we see in this and other courts, and it ended badly in this particular situation."

As a result of the ambush, the victim suffered stab wounds to the neck, left thigh and left hand, as well as a broken nose and various bruises.

He required surgery, and now has permanent scarring to the neck and other parts of his body.

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Both Wilson and Beath-Williams were arrested over the attack, and remanded in custody, in February 2021.

Wilson was apprehended in Tasmania after his girlfriend contacted police and told officers he had boasted about eating with the same knife he had once used to stab someone in Canberra.

While on remand, both men negotiated guilty pleas to charges less serious than the attempted murder allegation initially levelled at them.

Wilson pleaded guilty to charges of intentionally inflicting grievous bodily harm and aggravated robbery.

Beath-Williams, meanwhile, admitted being knowingly concerned in the reckless infliction of grievous bodily harm.

The 24-year-old had already served all but a week of his non-parole period before he was sentenced on February 2, meaning he became eligible for release from the Alexander Maconochie Centre last Wednesday.

Wilson will not be freed from Canberra's jail, under the terms of his backdated sentence, until June 2023 at the earliest.

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