A 17-year-old boy ditched a party to help his mate bash a man they believed to be a pedophile.
They went to the wrong home and attacked 45-year-old John Bourke, who was completely innocent and had brittle bone disease.
He died. One of the teens who participated in the attack was sentenced in Victoria's Supreme Court on Monday to three years in youth detention.
Now 19, he was acquitted of murder and a jury couldn't reach a verdict on an alternative manslaughter charge.
He ended up pleading guilty to home invasion and recklessly causing serious injury at Maryborough, northwest of Melbourne, in July 2018.
The teen cannot be named because he was 17 at the time. He and his 15-year-old mate wandered to Mr Bourke's house from a party.
The younger boy tried to kick in the door before stomping on and kicking the victim's head.
His accomplice punched Mr Bourke and stomped on his leg, but did not inflict the fatal blows.
Mr Bourke's brittle bone disease meant even a bump or knock could cause fractures.
He suffered about 400 of these throughout his life.
Justice Elizabeth Hollingworth said both boys behaved in a "cowardly and disgusting" way.
"It must have been obvious to you, even in your intoxicated state, that you were attacking a slightly built, disabled man who was only 133cm tall," the judge said in sentencing the 19-year-old.
"It must also have been obvious that he was utterly defenceless against an attack by two physically fit teenagers.
"The two of you kept going, even as he called out for you to stop the assault."
The older teen admitted drinking about nine stubbies before the attack. He later admitted they "got the wrong house".
Mr Bourke's heartbroken family called the boys "evil", "animals" and "sadistic thugs" during a previous court hearing.
The boy convicted of his murder is awaiting sentence.
His co-offender has already spent 736 days behind bars and this will count towards his sentence.