Joel Cauchi, 40, armed himself with a pigging knife when he launched his unprovoked attack at Sydney's Bondi Junction Westfield in April 2024.
In late-2019, his father told treating mental health professionals his son did not need to start taking anti-psychotics again after being weaned off them months earlier.
"Information given to his father who became adamant that he did not want his son to go on medication as it will kill him," a nurse's note read.
"Father spoke that he himself had been traumatised by demons when awake and hears voices and is not on medication."
A mental health nurse who treated Cauchi from 2019 to 2020 told an inquest on Monday this created a conflict because his mother wanted him to be re-medicated after raising concerns about his mental deterioration.
At the time, his psychiatrist wanted to restart the anti-psychotics in response to his mother's feedback.
Cauchi went on to kill six shoppers and injure 10 others during a psychotic episode at the Westfield mall before he was shot dead by NSW Police Inspector Amy Scott.
Diagnosed with schizophrenia as a teen, he had been successfully treated in the public and then the private system at a clinic in Toowoomba.
Cauchi's mother first raised concerns about her son's worsening symptoms in October 2019, three months after he was weaned off the medication.
While he presented well afterwards, potential signs of relapse surfaced, the nurse told the NSW Coroners Court.
This included extreme obsessive-compulsive disorder where he used half a cake of soap in a single shower and large numbers of notes left around his apartment.
She wrote that his mother had read notes about being under "Satanic control" and religious themes.
Despite these concerns, Cauchi still presented well at face-to-face appointments and over the phone, the nurse said.
There was no discussion in early-2020 about ensuring he still received treatment after moving to Brisbane.
As he left Toowoomba and was discharged from the clinic, he was completely detached from the mental health system just as the COVID-19 pandemic gripped the globe.
A second nurse who treated Cauchi from 2011 to 2017 and again in 2019 and 2020, described him as someone who diligently complied with his medication.
He was concerned in 2016 about a possible mental health decline, she told the court.
"He didn't want to get unwell," she said.
"He had anxiety around it."
There were no concerns raised at weekly meetings, as he was weaned off his anti-psychotics, the court was told.
The nurse's clinical notes reveal Cauchi complained about the side effects of the drugs.
He said he felt mentally clearer, and could focus on his studies and hobbies better as the dosage was lowered
She was shocked and had a visceral reaction when she heard the news of the tragedy.
"I vomited when I saw that it was him," the nurse told the court.
"It really doesn't make any sense."
The nurse said she had not heard of anyone who had been taken off clozapine, an anti-psychotic that Cauchi was on, without being put on something else.
She also said she was shocked that patients discharged from psychiatric clinics were sent back to their GPs to find further mental health support.
Instead, she recommended the Care Programme Approach used in the United Kingdom where people have a follow-up and are allocated a case worker after they leave a clinic.
The inquest continues on Tuesday.
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