Gangland killer Carl Williams, who was bashed to death in jail on Monday, thought he was safe behind bars, his lawyer says.
Rob Stary said Williams, one of the Melbourne underworld's most notorious figures, had no fears for his safety in the high security unit of Barwon Prison.
"On the contrary, being in the state's strictest regime where he was constantly monitored... we thought he was secure, he thought he was secure and the authorities thought that he was secure.
"There has obviously been a very, very serious lapse," he told the Nine Network.
Convicted killer Williams, 39, suffered serious head injuries in an apparent attack on Monday afternoon. He suffered a cardiac arrest and could not be revived.
Inmate charged with murder
Prison officers are reported to have taken 25 minutes to find the dying prisoner in his cell - a claim which is under investigation by Victoria Police and Corrections Victoria.
The state's police corruption watchdog, the Office of Police Integrity (OPI), is to oversee the inquiry into Williams' murder.
Director Michael Strong said the OPI would ensure any claims of police corruption in relation to the killing were properly investigated, and draw attention to any defects or insufficiencies in the police investigation.
Lawyer Mr Stary welcomed the OPI's involvement in the case.
"They bring with it a pool of expertise and various powers, including coercive powers of investigation," he said.
One of Williams' fellow inmates, a 36-year-old who cannot be named for legal reasons, has been charged with his murder.
He appeared before Geelong Magistrates' Court on Tuesday, via video link from prison.
