Joel Cauchi had fallen through the cracks of the mental health system when he armed himself with a knife and rampaged through Sydney's Bondi Junction Westfield on April 13, 2024.
Six people were killed and 10 others, including a nine-month-old girl, were injured before the 40-year-old was shot dead by police.
As an inquest into the tragic events began on Monday, counsel assisting Peggy Dwyer SC said Cauchi had not been treated for five years before the mass killing despite being diagnosed with schizophrenia as a teen.
Dr Dwyer called the 40-year-old's web browsing history before the attack "distressing".
"Mr Cauchi was preoccupied with weapons, with violence and with mass killing," she told the NSW Coroners Court.
This interest in death and murder included searches for serial killers and mass killings both in Australia and overseas including the Columbine High School shooting in 1999.
Notes on his phone included references to planning a strike at a mall while armed with a knife, the court was told.
The searches showed a man who was seriously unwell and who was far from his parents in Queensland, who had previously kept a rein on their son's behaviour, Dr Dwyer said.
Expert psychiatric evidence would show that Cauchi was "floridly psychotic" when walking through the Westfield, Dr Dwyer said.
As the five-week inquest continues, coroner Teresa O'Sullivan will examine Cauchi's background, including how police interacted with him during his largely transient lifestyle.
She will also look for any potential missteps in his mental health treatment after he was diagnosed with schizophrenia.
The response to the tragedy by security guards and the media will also be probed.
Ms O'Sullivan will then make findings at a later date about what happened and can suggest recommendations aimed at preventing similar events.
Dawn Singleton, 25, Ashlee Good, 38, Jade Young, 47, Pikria Darchia, 55, Yixuan Cheng, 27 and security guard Faraz Tahir, 30, died in the attacks.
A memorial established at Bondi Junction ahead of the mass killing's anniversary earlier in April contained photographs and floral tributes to those who had died.
Lifeline 13 11 14
beyondblue 1300 22 4636
13°C