The man who killed the suspected murderer of 16-year-old Larissa Beilby in a jailhouse attack has been sentenced to 11 years in prison.
Isaac Martin, 29, pleaded guilty to unlawful striking causing death after he hit Zlatko Sikorsky in the head at the Wolston Correctional Facility on November 10, 2020.
The 37-year-old died 10 days later from a traumatic brain injury.
Sikorsky was awaiting trial for the murder of his then-girlfriend in June 2018 at Buccan in Logan.
Ms Beilby's body was found stuffed in a barrel in the back of a ute on the Gold Coast, sparking a manhunt which ended two days later when Sikorsky was found on the Sunshine Coast.
In sentencing at Brisbane Supreme Court on Friday, Justice Martin Burns took into account Martin's early guilty plea, exposure to childhood abuse, and mental health issues, but said that needed to be balanced with the seriousness of the crime and community protection.
"This was a completely unprovoked attack that had a devastating outcome," he said.
"There is no evidence of remorse from your statements."
A psychiatric report noted Martin had a high risk of future violence which Justice Burns said he "had no difficulty in accepting".
Martin, who represented himself, will be required to serve 80 per cent of his sentence before he is eligible for parole.
Prosecutor Philip McCarthy KC told the court CCTV vision showed the pair standing outside their neighbouring cells while another prisoner's room was being searched.
They were talking amicably for a minute when Martin struck Sikorsky's head and neck.
Sikorsky swayed for 10 seconds and told another prisoner he was alright, before collapsing to the floor face first, hitting his head.
The cause of his death could not be attributed to the punch or the fall.
The court heard Martin walked out to the prison yard crying, telling other prisoners Sikorsky was his best mate, to apologise to him, and said that he didn't know what happened.
Later that afternoon, he told corrective officers it was an accident and he thought Sikorsky was trying to "stitch him up" and attacked him out of fear he would be hurt, and the deceased was trying to poison his food.
When told of Sikorsky's death by corrective service officers, Martin said "I don't give a f**k", before laughing and saying "It was karma for what he did to that young kid".
The prosecution highlighted a psychiatric report which showed Martin had psychopathic tendencies and a narcissistic personality, and prided himself on his violence.
Martin told the court he had undergone surgery in the days before the attack, after cutting an artery and losing more than a litre of blood.
He said he had heard his name around the prison and was scared he would be jumped by other men.
He had tried to get help from supervisors for his paranoia but the officers he talked to were not familiar with his recent surgery.
Martin said he didn't recall the moments prior to the attack, only shortly after, and still couldn't fully explain his actions.