Benjamin Glenn Hoffmann has pleaded not guilty to four counts of murder on June 4, 2019, saying he'd been poisoned and it had caused him to be "out of his mind".
Psychiatrist Robert Parker examined the 47-year-old a decade earlier after he moved in with his mother and concerns were raised with the mental health authorities.
"Ben had come back from Victoria and was having problems adjusting to life back with mum and this was causing behavioural difficulties," he told the Northern Territory Supreme Court on Thursday.
Prof Parker said Hoffmann's family had reported that he had been verbally abusive and threatening towards his mother and younger brother.
"Has been on the roof in the middle of the night running up and down yelling and screaming," he said, reading from medical notes made after Hoffmann was admitted to hospital.
"Would call attention to himself with the neighbours who were in fear of him. Reported to be carrying a knife hidden in his shorts."
Prof Parker also said Hoffmann's mother reported he had "set up booby traps around the house and gathered things that could be used as weapons".
Hoffmann also had a "fixed idea that is not based on reality that his ex-partner had left him for a Muslim man and his ex-mother-in-law had paid a hitman to kill him".
Prof Parker said Hoffmann's mother also reported that he was being "neglectful of his personal hygiene".
"His mother had got him to move outside and sleep on a li-lo," he said.
Hoffmann was admitted for observation in the Royal Darwin Hospital, where he falsely alleged his mother was sleeping with his 17-year-old brother.
Prof Parker said no significant psychiatric conditions, abnormal thought or perceptions or mood disorders, or psychosis were observed.
But Hoffmann was found to have an antisocial personality disorder.
"It's pervasive constant difficulties that are disabling for basically being a normal human being in the community," he said.
Hoffmann was likely to have experienced "difficulties in work, social relationships and when interacting with the law".
Prof Parker said Hoffmann also had anger management and relationship issues and he was estranged from his father at the time.
His former partner in Victoria had also feared violence before Hoffmann returned to Darwin and his family reported bullying behaviour going back a number of years.
His mother was advised to speak to police and seek an apprehended violence order.
Earlier, the court heard Hoffmann told Prof Parker he'd experienced hallucinations and heard voices in the months after the shootings in 2019.
These included a male prison guard's voice directing him to self-harm and his mother's voice.
"Even though I look healthy, I feel like my mind is f***ed," Hoffmann was reported to have said, according to notes taken at the examination in July.
Prof Parker again came to the conclusion Hoffmann wasn't suffering from psychosis and said there was no evidence he had been suffering hallucinations.
However, he said Hoffmann appeared to be struggling to adjust to prison life while he was on remand before his trial.
Prof Parker also said he found no signs that Hoffmann had been poisoned as he had claimed.
The court has heard Hoffmann, who has a history of illicit drug abuse, was high on methamphetamine during the rampage.
After the killings, Hoffmann told police he believed he'd been poisoned the night before and it had caused him to be "out of his mind" and temporarily insane.
The Crown says Hoffmann was searching for his ex-girlfriend, Kelly Collins, and a man she said she loved, Alex Deligiannis, when the shootings happened.
Hassan Baydoun, 33, Nigel Hellings, 75, Michael Sisois, 57 and Rob Courtney, 52, are the men killed.
Mr Deligiannis had previously visited three of the locations regularly.
The trial continues.
