A source has told the Herald Sun newspaper police and prison bosses have learnt that no jail officer was aware Williams had been bashed until 25 minutes after he was attacked with the stem of an exercise bike on Monday.
The gangland killer was pronounced dead by paramedics 17 minutes later.
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The source says the delay in reaching Williams has prompted investigators to consider checking prison officers' bank accounts for any suspicious or unexplained cash deposits.
A prisoner who can't be named for legal reasons faced court via video link yesterday charged with Williams' murder.
Meanwhile, Victoria's police corruption watchdog has announced it will oversee the investigation into the killing of Williams.
The Office of Police Integrity says it will undertake an ongoing oversight and review of the police investigation into the prison murder of Melbourne's most notorious underworld killer.
Hours after Victoria's police chief Simon Overland admitted there would be repercussions following Williams' murder the OPI announced it would step in.
