The head of the ministry now responsible for the Pike River mine says systemic failures, rather than incompetent or careless staff, may have led to the fatal blasts.
Twenty-nine men died after a series of explosions that began at the West Coast mine on 19 November 2010. Only two workers managed to get out to safety.
The independent report, commissioned by the Ministry of Business Innovation and Employment (MBIE) and released on Wednesday night, examines how the ministry's own systems and staff contributed to the tragedy.
The investigation began in November 2012 after the Royal Commission report into the explosions was released.
It involved interviews with staff from the former Department of Labour and Ministry of Economic Development, and also considered the departments' operating procedures.
MBIE chief executive David Smol says Pike Rivers Coal's initial mining permit was handled by the Economic Development Ministry in a light-handed way and, because of this, concerns about the miner's level of geological knowledge of the area didn't arise.
He says the ministry's policy at the time was to process such mining applications as quickly as possible, and health and safety considerations were explicitly excluded.
Mr Smol says the Department of Labour, as the mine's regulator, wasn't firm enough with Pike River Coal and in one instance failed to issue a prohibition notice when it should have.
He says no employment action is being taken against any staff responsible for assessing the mining permit.
