A grieving Whanganui father believes his daughter might be alive today if police had acted on red flags about her killer.

Mother-of-two Jo Pert was fatally stabbed in January 2016 while out jogging in the Auckland suburb of Remuera.

The Whanganui-born 41-year-old's death was the final act in a series of incidents involving Tevita Filo, which included following a couple in their car for 12 kilometres the night before while in possession of a knife.

Police last week released parts of the Filo case file, including a statement from one of the two people he followed the night before the killing.

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The file revealed Filo had a history of carrying weapons, and had been convicted of possessing a knife in a public place.

Detail of Filo's criminal history has shocked Ms Pert's father, Castlecliff engineer Kevin Pert. He said police had told him that Filo had no relevant prior history "whatsoever".

Mr Pert said: "They had nothing. I am actually stunned ... this is the first I've heard of it."

The statement from one of the people in the car followed by Filo details how the man looked "vacant and strange", and how he chased them at "a great rate of knots" as they tried to evade him.

When police intervened they removed a large kitchen knife and then let him go.

The release of the file comes just weeks after the Independent Police Conduct Authority released its findings on complaints into alleged police failings into the way they handled Filo - who was later found not guilty on a charge of murdering Ms Pert by reason of insanity. He is being treated for schizophrenia.

The authority's findings included that the officers should have made more inquiries into allegations Filo was following the couple, and the police dispatcher should have notified them Filo's car was being sought in relation to theft from a shop.

However their actions in just warning Filo and letting him go were justified, and couldn't be linked to Ms Pert's death, the authority ruled.

Mr Pert said while he and his wife Jan didn't blame police for their daughter's death, they were "disappointed" at the findings of the authority's report.

"There was a deficiency with the way the police acted. We just thought, if the police did a little bit more maybe Jo would have been still alive the next day.

"The guy followed those two people the night before for about 12 kilometres. Well, the way I think about that - that's actually stalking. That's a crime."

The complaints to the authority were laid by two people connected to Ms Pert - whose funeral was held at Raetihi - one a former police officer and friend.

Just hours after Ms Pert's death, police asked the couple followed by Filo for 12km to give statements about their ordeal.

The man, who was driving, was suspicious enough to note Filo's licence plate. After driving 300 metres he noticed Filo's car was following them, and he became suspicious after Filo failed to take a turn on to a main thoroughfare.

The couple diverted though a supermarket carpark in a bid to get rid of him but that didn't deter Filo, who did a U-turn and "came speeding into the carpark at a great rate of knots", the man told police.

"He came racing up behind us and didn't get [right behind] us but close enough that he could continue to follow. That's when I called the police ... I stopped trying to shake him off and was just killing time until the police arrived."