A Queensland prisoner with chronic mental illness who killed his cellmate after watching a Mad Max film has been jailed for at least 11 years.
Glenn Ryan Clarke, 46, pleaded guilty in the Brisbane Supreme Court on Wednesday to the manslaughter of Nicholas Paul Thomas Triggs, 27, at Borallon Training and Correctional Centre, west of Brisbane.
Clarke was originally charged with murder after tying a ligature around Mr Triggs's neck on June 9, 2019 and putting a plastic bag over his head while they were both in a cell.
Crown prosecutor Caroline Marco told the court she would not proceed with the murder charge due to Clarke, who suffered from schizophrenia, having an abnormality of the mind at the time of the killing.
Ms Marco said Clarke had a lengthy criminal history that mainly involved home burglaries and retail armed robbery to fund drug addictions.
Clarke was watching the film Mad Max: Fury Road the night before when he decided to kill Mr Triggs.
He used a safety razor to cut a ligature from bed linen, wrapped it five or six times around Mr Trigg's neck and dragged him from the top bunk onto the floor.
Clarke used a piece of plastic cutlery to twist the ligature and make it tighter in order to make sure Mr Triggs was dead.
He then lay down on his victim's bed and watched TV for the next few hours before calling the guards at 5am to tell them his cellmate was not breathing.
Ms Marco said Clarke committed "an unprovoked, brutal and sustained attack on a vulnerable person."
"It was well-planned and well-executed with no warning given," she said.
"Clarke continued his attack in the face of resistance until he achieved death and was certain of it."
Ms Marco said Clarke had fantasised for years about killing another inmate and regularly refused to take his medication, leading him to believe the world existed only in his imagination.
Clarke's barrister Joseph Briggs said his client's parents were in court to support their son.
"The one thing that is constant in the equation of this man's life is mental illness ... he lacks insight into how it is affected by his drug use," Mr Briggs said.
Justice Thomas Bradley said Clarke had left Mr Triggs' mother with a "raw wound ... that made her feel traumatised, helpless and lost".
Justice Bradley noted Clarke told police he killed Mr Triggs because he "thought it was cool and it might make (him) notorious".
"You broke the hyoid bone at the top of Mr Triggs's throat, indicating moderate to severe force," Justice Bradley said.
The judge said Clarke's lack of remorse and long-held fantasies about killing police upon release demonstrated a "risk of physical harm" to the community, but he also did not want to impose a "crushing" jail term.
Clarke was sentenced to 14 years imprisonment as a serious violent offender who will have to serve 80 per cent of his term before being eligible for parole.
