Victoria Police officers involved in deaths or serious injuries to the public are not properly investigated by the force due to "clear conflicts of interest" and most cases failed to include evidence from independent witnesses, a damning report has found.

The scathing review by the state's corruption watchdog, the Independent Broad-based Anti-corruption Commission, delivers another rebuke to force command, which is reeling from the recent resignation of assistant commissioner Brett Guerin.

Mr Guerin was responsible for Professional Standards Command, which investigates police officers, until he was exposed as the author of racist and obscene online posts.

Victoria Police was also embarrassed by the handling of assault allegations against two officers at Ballarat station, that was captured on CCTV and widely publicised.

An internal probe by Professional Standards Command in 2015 cleared the two officers of any criminal offences and overturned their suspensions despite an ongoing IBAC investigation that resulted in charges being laid last year.