CORRECTIONS Victoria failed in its duty to keep notorious underworld figure Carl Williams safe in Barwon Prison.
That's the key finding of Victorian Ombudsman George Brouwer, whose 163-page report into Williams' murder was tabled in the Victorian Parliament on Wednesday.
Williams was murdered by fellow inmate Matthew Johnson on April 19, 2010. The murder was captured on CCTV.
"Mr Williams' death raises important questions as to how it is possible that a high profile prisoner in Victoria's highest security prison unit could be killed with an unsecured metal pipe from an exercise bike, and that prison staff did not find out about the incident for some 27 minutes," the reports reads.
"This raises important concerns about the monitoring systems in place at Barwon Prison.
"As a result of my investigation, I consider that Corrections Victoria failed in its statutory duty to ensure Mr Williams' safety."
Williams agreed late in 2008 to become a witness in relation to murder charges against a former police officer and another individual.
In December 2008 Johnson sought permission to be placed in Barwon's Acacia Unit with Williams on the grounds the pair had developed a friendship. Williams wrote to Corrections Victoria supporting Johnson's request, which was approved in January 2009.
But Mr Brouwer's report reveals that earlier that month then Acting Commissioner Rod Wise warned Department of Justice secretary Penny Armytage of the risks Johnson posed to Williams.
" ... there is little doubt that Johnson is capable of causing Williams harm if he were to find out the true nature of Williams' cooperation with Police," Mr Wise wrote in the email.
Despite the risks both Mr Wise and Ms Armytage supported the placement of Johnson with Williams, on the condition the pair was ""carefully monitored".
The report reveals Mr Johnson was a leader of the notorious Prisoners of War gang - a group of prisoners operating within Victoria's correctional system responsible for a series of violent assaults on prisoners and prison officers, with a hatred for police informers.
"It was this history to which Mr Wise referred in his email," Mr Brouwer wrote.
"The concerns raised there were substantial.
"As Acting Commissioner he should have exercised caution and not recommended that Mr Johnson could be placed with Mr Williams."
Mr Brouwer also writes in his report of an "unprofessional culture" among prison officers at Barwon Prison, "particularly in the Acacia Unit".
"While the culture I identified at Barwon Prison has not been demonstrated to have contributed to Mr Williams' death, it certainly did not contribute to his safety," he wrote.
The Office of Correctional Services Review conducted its own investigation into Williams' death, the results of which were not made public.
"I decided that it was in the public interest to conduct an investigation into Corrections Victoria's management of Mr Williams while in custody at Barwon Prison," Mr Brouwer wrote in his report.
Johnson was sentenced to a minimum of 32 years' jail in December 2011 for Williams' murder.
Williams was serving a life sentence for ordering the murders of three people and conspiracy to murder a fourth.