The boy was found with a gunshot wound to his face and neck after police were called to a unit in Norwest, Sydney's north-west, at about 5pm on Monday. Paramedics treated him at the scene before he was rushed to hospital in a critical condition. Police said he died around 8pm on Thursday.
Five other people were in the unit at the time of the shooting but were not injured. Three 18-year-olds were arrested, but two were later released pending further inquiries. The third, Isaac Bechara, has been charged with concealing a serious indictable offence and remains before the courts. He was formally refused bail at a hearing on Tuesday, and the matter has been adjourned until next month.
A 43-year-old woman was also present, while a fifth person has not been located.
Initially, police told the community they did not believe the shooting was related to organised crime, but have since said they are investigating whether the men present had criminal links. Superintendent Naomi Moore said police had "engaged" with the boy's family before, adding: "A number of individuals that were inside the unit at the time are well known to NSW Police and their association with organised crime is being considered by investigators."
Moore also revealed that some of those present were "not co-operating with investigators" and that the firearm had not yet been recovered. A resident said police could be seen searching a nearby park and creek after the shooting.
Premier Chris Minns described the incident as an "incredibly distressing situation" and "a very tragic reminder of how dangerous guns are, often the people who are the victims of guns are innocent people."
The investigation is continuing.