Victoria Police, in an official statement, confirmed that homicide squad detectives are working to establish the relationship between the 12-year-old and the victim.
Police say the nature of their connection remains a key aspect of the ongoing investigation.
The Barkly Street apartment building was cordoned off with police tape on Thursday, restricting access as forensic officers combed the scene for crucial evidence that could shed light on the motive behind the stabbing.
Authorities are urging anyone with information about the incident or individuals who may possess CCTV or dashcam footage of the area to come forward. They can contact Crime Stoppers on 1800 333 000 or report the information online.
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