In July 2013, police said they would not file charges over the 2010 mine explosion on the West Coast as there was not enough evidence for manslaughter charges over the death of the 29 men underground.
Evidence could not directly link anyone to the cause of the blast.
The case was reopened in 2018 when the re-entry of the 'drift' or stone tunnel leading to the mine, began under the Pike River Recovery Agency.
Police later followed by sinking a series of boreholes, and then lowered cameras into the mine workings, entry to which is blocked by a massive rockfall at the end of the drift.
In an update to families this week, Detective Inspector Grant Wormald said the police team had been working with more than 100 witnesses to prepare comprehensive statements for each of them.
This included details from earlier statements and information gleaned during the investigation of Pike River Coal Company documents. This led to a lot of new questions and the need for clarification.
"Last week four staff travelled to Australia to meet with 45 of those witnesses. All have been engaging and supportive of the efforts being made," Det Insp Wormald said.
"Other staff have been on the West Coast this week and we will be finishing the final 30 witnesses in other parts of New Zealand in the next week or two."
Over the past five months, the investigation team had been finalising the interpretation of all the underground photos taken through the boreholes and working with experts.
There was still a considerable amount of work to do to prepare the file to go to the Crown Solicitor.
"I am comfortable that we are making very good progress towards establishing what happened and whether anyone can be held to account. Please continue to be patient in the knowledge that good progress is being made."
In his last public interview, former Pike River mine manager and later chief executive Peter Whittall - an Australian - was living on a $1.3 million lifestyle block in Wollongong, south of Sydney, where he was running a rest home. He was still there as recently as last Christmas.
Former chief executive Gordon Ward, who left the company just six weeks before the explosion, was last known to be running an IGA supermarket on Australia's Gold Coast as recently as 2022. He consistently refused to provide evidence to the Royal Commission of Inquiry.
John Dow, the Pike River Coal board chairman, did co-operate and was recently seen back on the West Coast.
The commission found the board's focus on meeting production targets had set the tone for executive managers and their subordinates: "Mr Dow's general attitude was that things were under control, unless told otherwise. This was not in accordance with the good governance responsibilities.
"Coupled with the approach taken by executive managers, this attitude exposed the workers at Pike River to health and safety risks."
Operations manager Doug White also co-operated with the inquiry. His last known job was in the mining industry in Australia.
Pike's statutory mine manager Steve Ellis was last working in the mining industry in Canada.
By last winter, the overall police operating cost of its Pike River inquiry was $19.972 million since 2018.
Eleven full-time equivalent police staff were assigned to the job.
When the Pike River Recovery Agency handed over the keys to the mine site to the Department of Conservation, it had spent $71 million on the 'recovery' effort, which looked inside the drift.
Therefore, efforts so far have cost $91 million.
