Deakin, 22, stabbed his grandmother Gail Winner at her Bega home, led police on two dangerous car chases and then fatally struck retired police officer Mick Horne with a hammer on June 1, 2018.

"It's ingrained in your DNA but I forgive you ... because that's what (Grandma) would have wanted," the relative told the NSW Supreme Court on Wednesday.

"No court decision will change the fact you killed, and in that moment ... at some point, you had a choice."

Deakin has pleaded not guilty by reason of mental illness to murdering Ms Winner and Mr Horne and seriously wounding his grandfather, Thomas Winner, with intent to murder.

The NSW Supreme Court trial was halted after prosecutors on Wednesday accepted that defence would be made out on the balance of probabilities.

Taking the opportunity to address the court and Deakin, a grandchild of Ms Winner spoke of the long-term toll of wondering "what you should have seen, what you should have done".

Mr Winner, aged in his early 70s, is now dying "a slower and more painful death you tried to give him, while he sits forever thinking that he didn't save his wife".

Deakin "chose" to order and consume drugs, refuse medical advice, build his muscles and arm himself with a knife, the relative said.

"No family history can absolve you of these decisions," she said.

Three psychiatrists gave evidence on Tuesday about the onset of Deakin's schizophrenia, including signs of the illness in the years before June 2018 and his uncle's struggle with the same condition.

While Deakin had cannabis in his system on June 1 and had suggested consumption of LSD, the experts agreed his slow recovery and subsequent response to antipsychotic medication would not have occurred if his psychosis on June 1 was drug-induced.

"That's the science and that's what has been teased out in the evidence," prosecutor Neil Adams SC said on Wednesday.

The Crown had sought to act as a contradictor, trying to establish if any doubt could be cast on the medical opinions supporting the mental illness defence.

"Having heard and teased out the evidence, the Crown is not in a position to cast doubt on that evidence," Mr Adams said.

Justice Robert Beech-Jones, who heard the trial without a jury, is expected to give his verdict and reasons on Friday.

The trial will resume unless he is adequately satisfied Deakin is not guilty by reason of mental illness.

The trial has heard Deakin was deemed "clearly psychotic" by a doctor soon after his arrest at gunpoint in Bournda on June 1.

Preoccupied with ideas of "thought injection, mind reading and ... the matrix", Deakin told authorities he'd thought Mr Horne was a demon and his grandparents were vampires.

He'd became enraged about a motorcycle being moved at the home he shared with his grandparents before stabbing both with a pen-knife.

Deakin, then 20, led police on two quickly-abandoned pursuits before encountering Mr Horne, a retired senior constable driving home with his wife.

Deakin snarled when approached asked what he was doing, blankly telling Mr Horne to "follow the code".

Another question resulted in Deakin sighing, removing a claw hammer from his backpack and striking his fleeing victim in the back of the head.

Mr Horne's wife - like Mr Winner an hour earlier - witnessed her spouse's final moments before watching Deakin drive away in the couple's car.

Australian Associated Press