The night before Tevita Filo killed Jo Pert, he was pulled over by police for following a couple in their car while carrying a weapon, but was let go with a warning.
He told the officers who pulled him over, he needed the weapon for his own self-defence.
Outside the High Court at Auckland today after Filo was found not guilty by reason of insanity of Pert's murder and indecently assaulting two other women, Detective Inspector Kevin Hooper told media the decision by those officers to not take him into custody was the right one.
"Police confiscated the [weapon] at the time and officers questioned him at length. They checked the police computer to see whether or not there were any alerts against his name. As we know now there were no alerts that Filo had any mental health issues or that he posed any danger to the public."
Hopper said based on the officers' assessment of the situation, they used their discretion and issued a roadside warning.
The next morning, he killed Pert because he believed he was following orders to get back to the "real world".
Justice Murray Gilbert found him not guilty by reason of insanity because he was incapable of understanding his actions were morally wrong due to his schizophrenia.
Hopper said in the 17 hours before he turned himself in to police at the Auckland Police Station on January 9, Filo committed a range of random offences against multiple victims.
"What he told us during his police interview about what his intentions were was chilling."
Pert's family and friends had lost someone in the "most horrific circumstances" and recognised the wider impact her death had on the community, he said.
"They're coping as well as may be expected. I do think that they're still going through the grieving process."
Hooper said police had also been in good contact with Filo's family who had been very co-operative throughout the process.