A man accused of murdering his girlfriend thinking she was a demon experienced psychotic episodes for months afterwards, a NSW jury has been told.
During the Newcastle Supreme Court trial of Jordan Brodie Miller on Tuesday, psychiatrist reports were read out detailing his behaviour in custody after his June 2020 arrest.
In July, Miller refused to take his anti-psychotic medication and was paranoid and delusional, seeing "glitches" in reality and believing that he had accessed special settings in his iPhone that could alter voices and give military commands due to his heightened senses.
Police found the body of Miller's girlfriend, Emerald Wardle, 18, in the ensuite bathroom of the main bedroom of a home in Metford, near Maitland, on June 20, 2020.
Miller, who was then 20, admits killing Ms Wardle but has pleaded not guilty to murdering her, claiming he was in a psychotic state at the time and did not intend to harm his girlfriend and could not be held criminally responsible .
Psychiatrist reports indicate Miller felt guilt at Ms Wardle's death, despite thinking she was a demon, because she had some semblance of his girlfriend.
Defence barrister Peter Krisenthal cross-examined Professor David Greenberg on what Miller's mental condition actually was.
While the Crown claims Miller had drug-induced psychosis, Mr Krisenthal suggested he suffered from schizophrenia which had lain dormant until being triggered by the LSD he took on June 9 as well as his chronic cannabis use.
Schizophrenia was associated with both capgras syndrome, where an individual thinks someone they know has been replaced by a duplicate, and polydipsia, or an unquenchable thirst, Mr Krisenthal said.
Miller was seen with sweaty palms asking for water the day before the killing and was thirsty during later psychologists' interviews, the jury heard.
Prof Greenberg said both capgras syndrome and polydipsia could be associated with drug use, and symptoms of drug-induced psychosis could sometimes still be experienced months after a substance was taken.
"In this case, Mr Miller's case, he has most of the criteria to fit in a substance-induced or a drug-induced psychosis. He has very little criteria to fit into schizophrenia," he told the jury.
Whether Miller was suffering from schizophrenia or drug induced psychosis when Ms Wardle was killed, he was acting under a "substantial impairment" at the time, the professor conceded.
Professor Flavie Waters did not give a clear-cut diagnosis of drug-induced psychosis, instead saying Miller was vulnerable to these types of episodes for a number of reasons, including his frequent cannabis use, and that the LSD had amplified symptoms that he may have previously been trying to squash.
"These all contributed together and in combination to add to an increased risk of him developing a psychotic illness ... which resulted in the homicide," she said.
The hearing continues.
