Police allege the teenager, 14, who cannot be named for legal reasons, threw about 15 rocks at the security guard, breaking his nose and causing bleeding to the membrane between his skull and brain.
Police also allege the teenager, and a co-accused, believed the security guard was a police officer, and gloated about the assault shortly after.
“It is very concerning that the accused assumed a member of Victoria Police was inside the vehicle parked at the Bottle O, this only seemed to further encourage the accused and co-accused to assault the victim,” a Children's Court was told last week.
“After the assault the accused and co-accused have been bragging and gloating to their friends about ‘bashing a copper'.”
A court heard the alleged incident occurred about 12.20 am on February 26 this year, following two thefts from the store in the days prior.
Police allege that about 7.20 pm on February 23 the accused and co-accused attended the Bottle-O Warehouse in Shepparton where they stole $175 worth of alcohol.
Some hours later, about 2.50 am on February 24, the pair allegedly returned to the store and used pieces of concrete to smash the front window before filling a trolley with $236 worth of alcohol and leaving the store.
Police allege the accused, who was on bail at the time, and co-accused also stole $175 worth of alcohol from Dan Murphy's in Shepparton on the evening of February 25.
Following these incidents police allege the teenager and co-accused committed a spate of vehicle thefts and aggravated burglaries across Wallan and Melbourne, which included the theft of a Ford Mustang, a Volkswagen Tiguan, a BMW station wagon and a Range Rover valued at more than $200 000.
The accused was arrested by police on March 3 this year where he gave a ‘no comment’ interview to all the allegations.
He is facing more than 40 charges which include robbery, intentionally causing injury, unlawful assault, committing an indictable offence while on bail, theft, dangerous driving, assaulting an emergency worker on duty, aggravated burglary and unlicensed driving.
Police told the court they opposed the teenager's bail, saying he continued to commit the same dangerous offences making him a "serious risk to the safety of the community".
“The accused continues to show complete disregard to abiding by his bail, continues to associate with his co-accused and does not seem to care about any form of intervention to stop his offending,” they said.
The teenager's lawyer told the court her client could be bailed to a residential care facility that he had previously been living at, and called a worker to the stand to testify.
The court heard the teenager and co-accused had been housed together at the facility prior to the offending, with the worker giving evidence that she was concerned about the pairing.
The court was told the teenager would be housed in a therapeutic residential care placement if bailed, which aimed to support him and best manage his behaviour.
The worker told the court the teenager was "polite" and engaged "quite well" with people when he had an established relationship with them.
“I believe he has good intentions — I just believe he is quite impulsive when it comes to committing crimes,” they said.
“He thrives in a structured, supportive environment.”
The teenager is expected to face a Children's Court again at a later date.
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