After playing cards with a youth worker in detention a 16-year-old used a piece of plastic fashioned into a makeshift weapon to try and rob him.
Then he was released on bail.
The teenager with a "bad criminal history" was in a central Queensland detention centre after trying to rob a 66-year-old man while on probation, Judge Jeffrey Clarke said in the Children's Court in Rockhampton.
He and others confronted the man on a narrow pedestrian walkway on a bridge over Rockhampton's Fitzroy River.
When the man said he didn't have money the group hit him before the teen kicked him at least six times in the head and ribs.
The man who held onto his shopping bags after being knocked down was left bleeding and swollen.
"He waited for you all to walk off and then made his own way home and then stayed, cowering in his own home for two days, before he had the confidence to go back out and report what you had done to him to police," Judge Clarke told the teen in sentencing him.
Months later the teen and another boy planned to rob a youth detention centre worker with sharpened plastic pieces with a makeshift handle.
After playing cards with the worker, they demanded keys, menaced him with the weapons and cornered him in a doorway, Judge Clarke said in sentencing remarks published on Thursday.
The worker was rescued when nine colleagues intervened.
Within three months of being released on bail in March the teen took car keys from a house before spraying lighter gas under a seat of the Mazda CX-5 and igniting it.
The teenager had already become institutionalised, having spent most of the previous two years and six months in detention and had been locked in his cell at times to control violent outbursts, according to a pre-sentence report.
He also used drugs, including methylamphetamine intravenously, and mind -altering substances.
"You are going to have to find a way to conduct yourself in a socially acceptable way, not be violent, not deal with other people's property, or destroy other people's property, because you are stressed, or because you are unhappy with how things have gone for you," Judge Clarke told the boy.
After pleading guilty to two counts of attempted armed robbery and one count of arson, Judge Clarke ordered the teen be detained for 18 months but serve half that time in detention.
He will be required to comply with conditions of a supervised release order.
