A man who set himself on fire after allegedly killing his father and a 12-year-old girl believed he had to commit the crimes to protect his mother from a bikie group that was threatening to kill them, a court has heard. Renzo Da-Pra, 48, is on trial in the NSW Supreme Court, charged with the murder of his father, Gino Da-Pra, 77, who was beaten to death and dumped in a car boot, and the girl whose throat was cut soon after. He is also charged with attempting to murder the girl's grandmother, by also cutting her throat. Advertisement: Story continues below Both deaths happened within hours of each other in the western Sydney suburb of Wetherill Park in December 2009. In his opening address to the jury, Crown prosecutor Ken McKay said Mr Da-Pra's mental state at the time of the alleged murders would be a crucial issue in the trial. Mr McKay said that Mr Da-Pra believed that a bikie group had made threats against his family and that, if he killed his father and himself, somehow his mother would be spared. He said that, after committing the killings, he had presented himself at Fairfield hospital, reeking of petrol and with a pad of paper that held a confession. Mr Da-Pra then went to the hospital car park, sat in a petrol soaked car and set it alight. He was pulled from the vehicle by police and survived, but suffered serious burns. The court heard that Mr Da-Pra's fears about the bikie group were a delusion. But psychiatrists who interviewed him after the killings found that he had an appreciation of what he had done. Mr McKay said that he also "had a recognition that what he was doing was wrong". He had told a psychiatrist that he went to the home of the girl and her grandmother to establish an alibi for his father's death by making it look as if there had been a home invasion. Mr McKay said Mr Da-Pra had pleaded not guilty by reason of mental illness. The court heard that, when ambulance officers arrived at the home of the 12-year-old girl and her grandmother, the older woman was unable to say who had attacked her because her vocal cords had been partly severed. "She used her finger to draw an 'R' shape in the air ... to indicate it was the accused." The grandmother is expected to give evidence in the trial. The trial, before Justice Robert Shallcross Hulme, continues.