Roberts stood trial the following year but the trial ended when the judge ruled that Roberts was not fit to continue.
The court heard how Roberts had been living with Samantha Rangiawha, a mother of seven, in a caravan in Otahuhu in 2005.
The pair had been sniffing solvents in the early hours of December 3 when Ms Rangiawha was thrown out of the caravan. Roberts punched her to the ground before taking a 23kg concrete block and dropping it on her head.
According to the police summary of facts, Roberts dropped the block on Ms Rangiawha's head two more times, caving in the left side of her skull. She died at the scene.
Ms Rangiawha's older sister, Eva Marama, had to identify the body.
Before reading her victim impact statement to the court, Ms Marama turned to Roberts and told him it was the first time in seven years she had been given the chance to talk to him. "I hope you take this to heart."
She told the court today that while her sister had enjoyed an occasional drink, it had been Roberts who got her into solvents and drugs.
"It was then that she started to change and she lost her children."
She said seeing Roberts' trial cut short had been hard on the family and they were only now getting some form of resolution.
"It was a massive relief to come to court and hear you admit to taking my sister's life."
She said Roberts will spend time at the Mason Clinic with "nice people" supporting him but she hoped he would spend some time in prison.
"It's an awful thought to know that Buddy will be out one day and [Ms Rangiawha] will still be dead."
Justice Courtney said the Mason Clinic was "no holiday".
