The man who bludgeoned Carl Williams to death has claimed the gangland boss offered him $200,000 to kill former Victorian detective Paul Dale. Barwon Prison inmate Matthew Johnson has taken the witness stand for the first time and has told the court Williams talked about murdering people like others talked about football. He has pleaded not guilty to the murder of Williams on the grounds of self defence. Johnson bludgeoned Williams to death with the stem of an exercise bike in their maximum-security prison last year. He said his relationship with Williams soured in the months before his death, but has denied having any problem with Williams helping police. The 38-year-old told the court Williams treated him badly and had to be the boss, even asking him on one occasion to murder Dale. He said Williams boasted of having 15 murders to his name. Johnson told the court Williams knew how to "push his buttons". He said there were "many times" when he would have loved to have punched Williams. But he told the court "if we ever got into a fist fight, I knew in my heart I'd have to kill him". Johnson said he lived in fear of Williams and kept a sandwich-maker as a weapon. He said he feared Williams would harm his family if he asked to be transferred to a different unit. Graphic footage Earlier on Monday, the jury was played graphic footage of the crime scene. The prison footage shows Williams lying on his back outside his cell wearing only red tracksuit pants and sneakers after emergency staff failed to revive him. Williams's head is battered, his eyes black and the footage shows a large amount of blood around his body and in his cell. The court was also shown a video of Johnson's first police interview after the incident. In it, Johnson responds to the questions with "no comment" and repeatedly tells detectives he acted alone. Head of security for Corrections Victoria, Bruce Polkinghorn, has told the court Johnson was the general of a group of inmates known as the Prisoners of War. Mr Polkinghorn said the group was known for its old-guard values, particularly when it came to inmates seen to be helping authorities.