Matthew Charles Johnson is alleged to have hit Williams eight times with the stem of a bike seat in Barwon Prison on April 19 this year, inflicting head injuries which led to his death.
Johnson had been sharing the prison's maximum-security Acacia Unit with Williams, who was serving 35 years for four murders.
Williams' former wife Roberta told the court on Friday he did not deserve to be killed in the way he was.
"Carl didn't do anything wrong to anyone to be bludgeoned to death the way he was," Ms Williams said.
Johnson's committal came after a three-day hearing in Geelong Magistrates Court in which it was revealed Williams had been assisting police in a corruption investigation at the time of his death.
The court also heard Williams had become so concerned fellow inmates would learn about his involvement with the police that he explained to Johnson what he was doing.
His father George Williams told the court on Thursday that Johnson did not like people who gave evidence against others.
George Williams said his son and Johnson, 37, had initially been good friends, but their relationship appeared to have begun to sour.
He said Carl Williams had been nervous and preoccupied on the day of his death after seeing a front-page newspaper story that revealed police were paying his daughter's school fees and had helped settle his father's tax bill.
Giving evidence via video, Ms Williams said her former husband had been happy to be in the same unit as Johnson.
But she noticed he was unsettled in a phone conversation they had on the day he died.
"Carl seemed agitated," she told the court on Friday.
Ms Williams, who was divorced from Williams, said the phone call was abridged.
"I cut Carl short on everything because I was in a hurry to get to this photo shoot (with a women's magazine)," she said.
She told the court she was "the angry one" in their relationship, even though she recounted an incident in which her then husband shot at her.
When asked about the incident she raised in her autobiography, she said they had argued over another woman in 2000 when she was pregnant with their child.
"He got a little bit annoyed and shot at my car," Ms Williams said.
Magistrate Rosemary Carlin ruled enough evidence existence to support a conviction and remanded Johnson in custody to appear in the Supreme Court in Melbourne on January 19 for a directions hearing.
