The department in charge of workplace safety did not investigate the Anzac Day air force crash because it misunderstood the law it enforces, a government legal review has found.
An inquiry will start this week into the Department of Labour's failure to investigate health and safety issues behind the 2010 helicopter accident that killed three Royal New Zealand Air Force servicemen.
But the inquiry will not investigate the actual health and safety failures - prosecution for breaches is no longer possible because the time limit has passed.
Andrew Carson, whose son Ben died in the crash, said he would make a complaint to the police in a bid to make someone responsible for the death of the three men.
"If it had been any other company in New Zealand, these people would have been investigated and either found responsible or not to blame."
The new inquiry comes after Defence Minister Jonathan Coleman ordered a review of the safety improvements following the crash.
As State Services Minister, Dr Coleman will now announce a second inquiry into health and safety enforcers' mistaken rejection of their responsibility to investigate the crash.
Yesterday, staff at his office said details of both inquiries would be announced this week.
The Herald has learned the mistake occurred because the Department of Labour - now part of the Ministry of Business, Innovation and Enterprise - believed its responsibility to investigate workplace accidents - including those in the military - did not extend to those involving aircraft.
It referred the accident to the Civil Aviation Authority (CAA), which investigates aircraft crashes.
The CAA told the department it had no jurisdiction over military accidents - and no investigation was undertaken by either party.
The ministry's health and safety head, Brett Murray, said last night: "Crown Law has determined that the department did have jurisdiction to investigate". In future military aviation accidents, "the ministry would lead the investigation with support from the CAA".
The error led to Dr Coleman being given incorrect advice, which he repeated in a letter sent in February this year to the Carson family, who had written asking why the air force was allowed to investigate itself.
Dr Coleman replied " ... the Department of Labour does not investigate events involving the operation of aircraft."
He said the military "must have its own airworthiness and flight safety processes around military flying regimes and tasks".
Dr Coleman was told about three weeks ago that he had been wrongly advised.
Yesterday, he would not be interviewed, but an official in his office said State Services Commissioner Iain Rennie was setting up an inquiry to find out how the mistake had happened and to make sure it was not repeated.
Mr Murray said the issue emerged after the Carson family questioned the lack of a health and safety inquiry.
Two weeks ago, Mr Murray met the CAA, the Carsons and lawyers acting for survivor Sergeant Stevin Creeggan, who is suing the air force over health and safety failures.
At the meeting, Mr Murray said he explained the confusion.
Mr Carson said he was told the time limit for a health and safety investigation had passed.
"The inquiry the air force was conducting was nothing to do with health and safety. It was focused on the squadron and the cause of the accident."
The air force review was carried out on the basis it would not find fault.
It revealed a tangled chain of command and flouting of safety-based orders amid a culture of risk-taking with over-stretched safety systems.