Jordan Miller was in 2022 found guilty of murdering Ms Wardle, a jury finding the psychosis he was suffering at the time of her death was caused "solely" by using LSD and cannabis.

But after four years spent behind bars, and in the absence of illicit drugs, the symptoms of an underlying mental illness persist, prompting two psychiatrists to diagnose Miller with schizophrenia.

And it was those further symptoms in the years after Ms Wardle's death, that fresh psychiatric evidence, accepted by prosecutors, that confirmed that what Miller was suffering from in June 2020 when he killed Ms Wardle was a first episode of psychosis arising from schizophrenia, which was not caused solely by using drugs.

And on Friday in the Court of Criminal Appeal, Miller's conviction for murder was overturned and its place the court entered a special verdict of act proven but not criminally responsible.

Miller was referred to the Mental Health Review Tribunal and will remain behind bars until he no longer remains a threat to himself or others.

The Newcastle Herald reported last month that Miller had launched an appeal against his conviction and a hearing last Friday was initially expected to take a full day and hear evidence from as many as four experts on the subject of the cause of Miller's psychosis.

Instead, after Miller's treating psychiatrist Dr Natasha Rae and forensic psychiatrist Dr Olav Nielssen both diagnosed him with schizophrenia, and the prosecution's expert agreed, the hearing lasted only about 20 minutes before the CCA reserved its judgment.

After a quick turnaround, the CCA delivered its judgment on Friday morning, upholding the appeal and quashing the conviction.

The Herald revealed last week that the key grounds of appeal were that there was a miscarriage of justice due to fresh evidence of the emergence of further symptoms after the trial and the subsequent diagnosis of schizophrenia.

The issue at trial was not whether Miller killed Ms Wardle, but whether the psychosis he was suffering at the time was caused "solely" by using drugs or as a result of an underlying mental illness.

Both experts at trial agreed that if further symptoms emerged in the future then Miller should be diagnosed with schizophrenia, meaning the psychosis he was suffering at the time of the killing was not caused solely by using drugs and he should not have been found guilty of murder.

"In this case, the fresh evidence goes to the root of the critical factual issue at trial," Public Defender Richard Wilson SC said in written submissions. "It is submitted that it is not only credible but cogent and compelling. "In combination with the undisputed evidence at trial, the fresh evidence cogently supports a special verdict. "Its unavailability means that there has been a miscarriage of justice."

As the Newcastle Herald has reported previously, there was no history of domestic violence between the couple and Miller - a university student working part-time - had no criminal record.

Instead, he was in a psychotic state and had lost touch with reality causing him to believe Ms Wardle - the woman he was in a loving relationship with - was a "demon" who was "sucking the life out of him."

There was no dispute during the trial that it was Miller who had killed Ms Wardle.

He confessed; first to police and then during his first appearance in court, repeatedly saying: "I am a murderer."

And the medical experts called to give evidence agreed he was in a psychotic state at the time of the killing.

The only issue for the jury to determine was what caused him to be in that psychotic state and made him believe he had no choice but to kill the young woman he loved.

Miller pleaded not guilty to murder and raised a defence of mental health impairment, with Dr Nielssen giving evidence that he was suffering a first episode of psychosis in the form of an underlying chronic schizophrenia, which was not caused solely by drug use.

Meanwhile, the prosecution said the psychosis Miller was suffering at the time of the killing was caused solely by using LSD and cannabis.

Professor David Greenberg opined Miller's psychotic episode was "temporary", related to his use of drugs and it was too early to definitively diagnose him with schizophrenia.

And after deliberating for about 12 hours the jury rejected the evidence of Dr Nielssen and agreed with the prosecution, finding Miller guilty of murder.

He was later jailed for a maximum of 20 years, with a non-parole period of 13 years and before Friday's decision was not eligible for parole until 2033.

But the jury didn't have the benefit of the fresh evidence, it wasn't available and could only be determined through the passage of time.

"Had this evidence been available at trial the jury would almost inevitably have returned a special verdict," Mr Wilson said.