Victoria's top corrections official says he's never heard of his guards playing indoor cricket while on duty, let alone before gangland killer Carl Williams was bashed to death.

Guards at Barwon Prison near Geelong did not see the attack in the Acacia unit on closed-circuit television although it was captured by CCTV cameras.

The Herald Sun newspaper reported on Tuesday that guards had been known to play indoor cricket while on duty.

The newspaper said there was no suggestion cricket matches were a factor in the killing of Williams in April, but it said Corrections Victoria management was alarmed by news of the cricket match and has warned staff there should be no repeat of the practice.

Corrections Victoria Commissioner Bob Hastings said he did not know about any cricket matches.

"I don't know whether this is accurate," he told ABC Radio in Melbourne on Tuesday.

"This is news to me. This should be and will be part of the investigations and it should be flushed out."

A previously leaked autopsy report revealed that Williams' absence was not noticed for 30 minutes.

A fellow inmate has been charged with bashing Williams to death, using the stem of an exercise bike.

Mr Hastings said procedures had been changed since the Williams slaying but he could not comment further until investigations were completed and made public.

"We're constantly reviewing how we do business," he said.

"Coming out of this incident we went back and looked at some of our processes and some of our procedures and what we could improve and certainly that's been undertaken as part of a management regime down at Barwon."

Four investigations were launched into the slaying, including one by the state's corrections watchdog, the Office of Correctional Services Review, as well as a police investigation, Taskforce Driver, overseen by the police watchdog, the Office of Police Integrity