An aspiring rapper who bashed a sleeping man to death was in a state of "psychotic delusion" heightened by months of drug use, a court has been told.
Coskun Jaques Marius, 30, in November pleaded guilty in Brisbane Supreme Court to the manslaughter of Tane Tahi Manawa, 38, at the victim's Surfers Paradise home on May 10, 2019.
Marius pleaded not guilty to the murder of Mr Manawa on the grounds of having an abnormality of the mind at the time, and the matter was taken to trial over the past two weeks.
Barrister Lars Falcongreen, acting for Marius, told the jury in his closing statement on Tuesday that the only real issue in the trial was deciding whether his client had diminished responsibility for Manawa's death.
Mr Falcongreen said Marius had chosen to testify in his own defence when he was perfectly entitled to say nothing and let hours of material from police and psychiatrists speak for him about his mental state.
"Was (Marius) shaken to great extent during the hours of being grilled by the prosecution ... I suggest his account is credible and reliable," Mr Falcongreen said.
Marius had testified that he had developed an alter-ego called 'Si3ge' as a protective figure in response to being bullied at school, whom he experienced as both an internal and external voice.
Mr Falcongreen said Marius saw himself as Si3ge when he attacked Mr Manawa, being unable to remember arming himself with a metal bar from a home gym and striking the repeated blows to Mr Manawa's head as he reclined in an armchair.
Marius said he had been homeless, unemployed and using methamphetamine in the months prior to the killing, but Mr Manawa had offered him accommodation in return for performing housework.
The jury heard claims Mr Manawa, known to his friends as Dre, had later turned abusive and violent towards Marius.
Marius said he formed the belief that Dre had been drugging and sexually assaulting women, including a close family member.
Mr Falcongreen said forensic psychiatrists had agreed Marius had been feeling paranoid and victimised at the time of the attack on Dre, with symptoms of either "psychotic delusions" or schizophrenia.
In his closing statement, crown prosecutor Michael Lehane told the jury they had heard evidence from the "crème de la crème of psychiatry in Queensland" and those experts had dismissed Si3ge as the "stuff of Hollywood" or a product of Marius's unexpressed aggression.
"Coskun Jaques Marius, CJ Marius and Si3ge are one person, who murdered a defenceless man as he slept," Mr Lehane said.
Mr Lehane told the jury they could look at Marius's deliberate actions taken before and after Dre's death, including multiple lies told to his housemates, which could lead them to conclude Marius was aware and in control of his actions and knew they were wrong.
The jury was due to start deliberation on Wednesday after receiving instructions from Justice Glenn Martin.
