A Sydney man who now denies murdering a schoolgirl in 1998 was most likely suffering from schizoaffective disorder at the time he confessed to police, a jury has been told.
Vinzent Tarantino, 52, has pleaded not guilty in the NSW Supreme Court to murdering Quanne Diec, 12, who vanished on July 27 in 1998 after leaving her Granville home to walk to the train station on her way to school.
Her body has never been found.
Tarantino's lawyer, Belinda Rigg SC, previously told the jury her client made false admissions to the crime because he feared for his life and believed he was being pursued by bikies who had threatened him and his loved ones.
The jury on Friday heard evidence from two forensic psychiatrists and one clinical and forensic psychologist on Tarantino's mental state in November 2016, when he confessed to Quanne's murder.
Appearing in the witness box together, all three experts - one for the prosecution and two for the defence - agreed Tarantino had been suffering from a psychotic condition for almost 20 years.
Forensic psychiatrist Dr Andrew Ellis told the court this was "most likely schizoaffective disorder" - a long-term mental illness characterised by delusions or hallucinations.
Ms Rigg had previously told the jury her client did not consider himself mentally ill. As Dr Ellis gave his opinion, Tarantino shook his head in the dock.
The experts contended in court that Tarantino was suffering from the delusional belief that the only way to ensure his safety and his family's salvation from bikies, was to confess to Quanne's murder.
"To protect himself either by going to prison and protecting his loved ones because the bikies would be placated by this action," Dr Ellis said.
In the period leading up to his confession, the experts said Tarantino became increasingly delusional and paranoid.
All three agreed that there was no difference between someone who thinks their life is under threat and someone who thinks that because of a mental illness.
"When someone has a delusional thought they have no way of telling it apart from other thoughts that they have," Dr Ellis said.
"There is a significant amount of information that the threats did not occur but his belief that they did was consistent."
After the jury heard that expert opinion, prosecutor Pat Barrett questioned Dr Ellis over whether he could offer an explanation for the confession Tarantino gave his brother before handing himself into police.
Mr Barrett said Tarantino told his brother 'I killed a kid'."
"I see that statement to be part of any of the potential explanations. It could be a delusional belief. It could be part of a lie or it could be a genuine memory of being involved in the murder," Dr Ellis said.
The trial is continuing before Justice Robert Beech-Jones.