A university student feared his girlfriend was a demon when he strangled her to death, a NSW court has been told.
When police arrived at the scene, Jordan Brodie Miller ran towards them pleading for help and tried to get into the police car.
Crown prosecutor Lee Carr told a Supreme Court jury in Newcastle on Wednesday how Miller told police: "If you walk inside and go into the bathroom, it's in there, the demon. Help me, help me, the demon's got me, help me."
Miller claimed a cut to his hand had been caused by the demon.
Police found the body of Miller's girlfriend, Emerald Wardle, 18, in the ensuite bathroom of the main bedroom at the home in Metford, near Maitland, on June 20, 2020.
After his arrest, Miller, aged 20 at the time, admitted taking LSD 11 days earlier and claimed to have reached spiritual enlightenment but Emerald had been "trying to suck the life out of me".
Mr Carr said just before midnight on June 9, a concerned Ms Wardle called a friend for advice as to how she should act around people on acid because "Jordan's on it right now and I don't know how to respond or behave. He has said and done a couple of weird things".
Miller 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 .
Mr Carr said Miller had been a regular cannabis smoker with no history of mental illness and the real question for the jury was what caused him to be in a psychotic state when he killed Ms Wardle.
He said the jury had to decide if the killing was caused by a drug-induced or substance-induced psychosis or if, as the defence claimed, it was the first episode of psychosis caused by an underlying form of chronic, undiagnosed schizophrenia.
The prosecutor said psychiatric evidence to be called by the Crown would say Miller's use of drugs and the lack of any early signs of a psychosis pointed to the killing being drug-induced, meaning Miller was guilty of murder.
Outlining what happened on the night Ms Wardle was killed, Mr Carr said a neighbour heard muffled yelling at 12.12am where the male sounded angry and the female sounded frightened before there was a loud bang like a door slamming.
Miller was speaking to a triple-zero operator some time later and said: "This is an emergency. I feel like my health is at risk."
He wanted someone to come quickly to the house because he said there was quite a mess at the property.
"They're going white," he told the operator.
"They're starting to bleed from their mouth."
When asked who he was talking about, Miller replied: "The person that I killed. I believe it's a demon. I killed a demon, yes."
At 1.15am Miller, a part-time employee at Caltex service station at Raymond Terrace, called a counselling service for Caltex employees and asked them to please send help because he had just killed a demon.
"I killed a demon. I don't want to have my throat on its neck the whole entire night, please send someone,'' Miller said.
When police arrived Miller was standing outside near the gate wearing tracksuit pants and no shirt or shoes.
Defence barrister Peter Krisenthal said there was no question Miller had been in a psychotic state and didn't understand what he had done.
Mr Krisenthal said family and friends referred to Miller as a gentle giant and goofy who wouldn't hurt anything or anyone.
Psychiatric evidence called by the defence would indicate his drug use was not likely to have been significant in causing his downward spiral into psychosis.
The trial before Justice Richard Cavanagh resumes on Thursday.
