Police have charged a man with the murder of Melbourne gangland killer Carl Williams at a prison in Victoria.
Williams, the Melbourne underworld figure who was serving 35 years in jail for four murders, was bashed to death with part of an exercise bike inside a maximum security unit at Barwon Prison in Geelong on Monday, the ABC reports.
The 39-year-old went into cardiac arrest after suffering head injuries.
Victoria Police Chief Commissioner Simon Overland says Deputy Police Commissioner Sir Ken Jones is leading the police investigation.
Mr Overland told the ABC that police are working to ensure no other prisoners are at risk.
Williams was sentenced to jail in 2007 for the murders of gangland rivals - father and son Lewis and Jason Moran, Mark Amelia and Michael Marshall - and conspiracy to murder another man during Melbourne's underworld war.
The television series Underbelly is based on the gangland killings.