Joel Cauchi, 40, had been diagnosed with schizophrenia as a teen and was experiencing psychotic symptoms when he killed six people and injured 10 at Sydney's Westfield Bondi Junction in April 2024.
An inquest has been told Queensland police had a number of chances that could have been used to reconnect him to the mental health system.
Cauchi, who was shot dead by police during his stabbing rampage, had stopped taking his medication in 2019 and ceased seeing a psychiatrist in 2020.
In the years after that, Cauchi had numerous interactions with Queensland police, including at his parents' home in Toowoomba in January 2023.
At that call-out, he accused his father Andrew of stealing his collection of knives, telling attending officers that they had to be returned or he would become bankrupt or homeless.
That moment has been described by an expert psychiatrist who will give evidence at the inquest as a "missed opportunity".
While a follow-up visit to the Cauchi family home was requested, the state's police mental health incident co-ordinator saw the email but forgot to action it due to an "oversight".
The coroners court has also heard that in May 2021, police were called to Cauchi's unit in Brisbane after residents heard a man screaming and the sound of someone being hit.
He told attending officers that he had been slamming his fridge.
Cauchi was also pulled over three times in 2020 and 2021 by highway patrol police for erratic driving, the court heard.
The coroner will hear further evidence on Tuesday about what Queensland police could have done to make sure Cauchi was able to receive the treatment he required.
Witnesses include a police officer working as a mental health intervention staff member in Toowoomba and the wider Darling Downs region.
Inspector Bernard Quinlan, manager of the Queensland police force's vulnerable persons group, will also take the stand.
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