The police investigation began the day after the November 2010 explosion killed 29 men, more than 2.5 years ago.
The investigation determined there was insufficient evidence to lay manslaughter charges against anyone involved in the management of Pike River Coal Limited prior to the tragedy.
“The lack of any causative link to the specific events which led to the explosion means a manslaughter prosecution of any individual does not meet the standard of evidential sufficiency,” a police statement Thursday evening said.
Detective-Superintendent Peter Read, who led the inquiry, said it was a difficult decision that police did not take lightly.
“I informed the families of the 29 men this evening and I know they will be very disappointed. I can only give them my absolute assurance that we have been meticulous in our investigation and consulted widely as the inquiry progressed.”
Police said they could lay a charge of criminal nuisance, but it would interfere with prosecutions being pursued by the government.
“At this time police believe this matter is most appropriately dealt with through the health and safety prosecutions led by the Ministry of Business, Innovation and Employment,” Read said.
Pike Rive Coal Limited was ordered last month to pay almost $A3 million in compensation and fines after being found guilty of nine health-and-safety charges.
PRC’s CEO at the time of the explosion, Peter Whittall, had 12 charges laid against him under the Health and Safety in Employment Act.
Read added that the investigation was one of the most complex undertaken by police. It involved formal interviews with 284 individuals, 25,000 pages of witness statement transcripts and some 34 million pages of documentation relating to the operation of the mine.
Up to 16 police investigators were involved at any one time, a range of experts provided technical input and advice was sought from Crown Law and the Crown Solicitor.
The superintendent said that the decision was based on currently available information and there may be a chance that the case could be reopened if more information became available.
“It is possible that at some point in the future re-entry to the mine might be achieved allowing a scene examination to be completed,” Read said.
"However, I stress there is no certainty that this would produce any new relevant information. Even if new information was identified, there is no guarantee that it would lead to a future prosecution.”