The Mickleham boy was found critically injured outside Craigieburn Community Hospital in Melbourne's north about 7.50pm on Wednesday.
A staff member from the clinic rushed to his aid and delivered CPR, but he died at the scene.
Police have made multiple arrests in the days since, beginning with the arrest of a boy, 16, and man, 20, in Pascoe Vale early on Thursday.
The 16-year-old, who is from the Goulburn Valley area, has since been charged with murder and remanded to appear in a children's court at a later date.
The 20-year-old man, from Beveridge, was charged with criminal damage by fire and bailed to appear at Broadmeadows Magistrates Court at a later date.
On Friday, police announced they had made further arrests as part of the same investigation.
A 15-year-old girl from the Fawkner area was arrested overnight and charged with affray and theft of a motor vehicle.
She was bailed to appear in a children's court at a later date.
Meanwhile, a 15-year-old Craigieburn boy was arrested on Friday morning to be interviewed.
The investigation is ongoing.
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