Most complaints from Aboriginal Victorians about police behaviour are backed by evidence but only a fraction are officially substantiated by the force, an audit has found.
The Independent Broad‑based Anti‑corruption Commission, Victoria's police oversight body, examined the force's handling of 41 complaints made by Aboriginal people and its oversight of 13 serious incidents involving an Indigenous person.
Of the audited complaints, 41 per cent involved those aged 17 or younger and almost half (46 per cent) were related to the use of force or assaults by police, often during an arrest.
The other most common allegations concerned human rights breaches (21 per cent), duty failures (11 per cent) and improper language or harassment (10 per cent).
IBAC said 27 of the 41 audited complaints were classified in a way that a determination of "substantiated" could be found.
But Victoria Police instead ruled only three were substantiated, two of which were connected to inappropriate language and the other duty failure.
"No complaint alleging assault was found to be substantiated, despite this being the most common allegation examined in this audit," reads the report, released on Wednesday.
Further, IBAC found 22 per cent of audited files contained "concerning indications" of bias or a lack of impartiality from officers involved in an incident.
Examples included officers dismissing a complainant's concerns, implying they were untruthful, and commenting on previous irrelevant interactions.
That figure jumped to 41 per cent for investigators, who IBAC suggested minimised the seriousness of allegations, downplayed officers' conduct, made inappropriate comments about civilian witnesses, and scrutinised the complainant's background or criminal history.
Despite conflict of interest forms being attached to 84 per cent of audited files, IBAC highlighted deficiencies in how Victoria Police identified and managed those conflicts in half of them.
In some cases, investigators worked at the same station or police service area as the officers they were investigating, while in others conflicts were declared but no action taken.
Other issues included inconsistencies in how the force recorded Aboriginal status, a failure to keep complainants updated on the probe's progress, and investigators not using dedicated existing resources to assist with complaints and serious incidents.
IBAC Commissioner Robert Redlich said the findings highlighted systemic and longstanding failures within Victoria Police's complaints-handling processes.
Among the report's 10 recommendations, the force has been urged to establish a dedicated system to deal with future police complaints made by Aboriginal people.
"IBAC has already made a number of recommendations for improvement and is committed to working with Victoria Police to implement recommendations for reform," Mr Redlich said in a statement.
Victoria Police have been approached for comment.