The officer who decided not to prosecute a bus driver over a crash on Mount Ruapehu that killed an 11-year-old girl says his recommendation would probably be different, knowing what he knows now.
The inquest for Hannah Francis, who died in July 2018 when the shuttle bus she was on crashed and rolled descending the mountain, is now in its third day.
A police report concluded it was highly likely the driver's actions caused the crash which left Hannah dead and 18 people injured, but no charges were ever laid.
Hannah's father, Matt Francis, was on the bus with her and attempted mouth-to-mouth resuscitation to save her.
At the inquest, Francis asked Inspector Neil Forlong only one question.
"Going back to your recommendation to not prosecute the driver, knowing then what you now know, would that recommendation be any different?"
"Yes, it probably would have," Forlong replied.
The bus lost its brakes and crashed into a bank at between 60km/h and 70km/h, coming to a halt on its side.
The driver, who gave evidence earlier in the inquest, cannot be named.
It was accepted brake failure led to the crash, but the cause of the brake failure was in dispute. The driver said the brakes worked fine at the beginning of the trip and he did not know why they later failed.
The brake type on the bus was air over hydraulic. To brake effectively, the bus needed air flow to recharge the compressed air tanks, which then flowed to the brakes when the pedal was depressed.
Senior Constable Chris Pelosi said the police report concluded the driver missed a gear change and repeatedly overused the brakes, which depleted the air supply so they failed.
The report found neither environmental factors nor mechanical failures could be blamed.
However, Forlong decided not to lay charges.
Central to that choice was whether or not a control switch was turned on accidentally by the driver, which would have dumped all the air in the tanks over about 20 or 30 seconds, quickly leaving the brakes powerless.
The switch was found in the off position at the crash site and there was some air remaining in the tanks.
Crown lawyer David Boldt said this meant the switch would have had to be turned on and off again by accident.
Forlong said whether or not the switch was ever turned on was the only piece of evidence he did not think police could prove beyond reasonable doubt, as required in a criminal court to achieve a guilty verdict.
The switch was not near any other driving controls, but next to the switch that closed the doors, so may have been turned on by mistake when the driver shut the doors at the beginning of the descent, Forlong said.
"While it is highly likely this crash was caused by driver error, that has drained the air tank and rendered the brakes ineffective, I cannot conclusively negate the defence that [the driver] hasn't inadvertently activated the ancillary switch causing the air to be dumped from the tank," Forlong read from an email he sent in 2018.
"My recommendation therefore is that there is insufficient evidence to charge [the driver] with any offence under the Land Transport Act," he read out to the court.
Forlong said he knew the decision not to lay charges would attract significant scrutiny and that there could be concern about why no person or company was held accountable.
He had sought in-house legal advice about whether or not the driver should be prosecuted. The legal opinion was that no charges should be laid.
"It wasn't a decision I came to lightly, it wasn't a decision I was 100 percent comfortable with at any time.
"And look, if it's the wrong decision I have no problems with apologising to the family for that now, personally apologising for that mistake," Forlong said.
Hannah's parents were sitting a few metres away, in Forlong's eye line.
Crown lawyer Boldt asked if Forlong could have failed to realise the significance of evidence that pressure in the reservoir tanks was fairly even after the crash, suggesting the switch was never activated.
"I don't have a mechanical qualification or a particularly mechanically-working brain, if you like, so it is something I could have overlooked," Forlong said.
He would have found it helpful if experts compiling the report had explained the complexities of important matters more simply, he said.
The inquest continues.