The growing sophistication of the police inquiry into the disaster was recently revealed by police counsel Simon Moore at the preliminary hearing of the Royal Commission.

“I'm instructed that to date over 200 witnesses have been interviewed, literally thousands of pages already of transcript,” he told the commission.

“Another 170 to about 200 witnesses are yet to be interviewed. There are at least 20 witnesses who are presently offshore and there is a police team leaving to interview those in Australia and elsewhere.”

Police have started cloning Pike River Coal’s servers, which will allow investigators to even delve into deleted emails.

About 30 million documents are expected to be copied in this process.

The New Zealand Police also revealed that the investigations were expected to end in August, which could then result in a decision to start criminal prosecutions, depending on the supporting evidence gathered.

The Engineering, Printing and Manufacturing Union represents coal miners in the country, and its national secretary Andrew Little believes that prosecutions pose a real risk to the Royal Commission.

He is concerned they could affect the commission’s ability to quickly come up with some findings, especially in relation to deeper causes of the disaster, such as the country’s underground coal mining regulations.

“Whether or not they prosecute, there is not much the Royal Commission can get into in relation to issues of Pike River management and what happened on the day,” Little told ILN.

“Because no one wants to give evidence on those issues while there is a possibility of prosecution.”

He said the police and Department of Labour inquiries into the disaster, even if they led to prosecutions, only looked at very narrow issues.

“They don’t get into the issues of what are the deeper problems in terms of the quality of regulation and the culture of management,” Little said.

“From a union’s point of view, we are keen for a quick, thorough examination of the regulations that apply here and whether or not they are adequate.

“It’s pretty clear they are already of a lower standard compared to Queensland and New South Wales, and if we want to improve the quality of legislation we need the Royal Commission to be doing that exercise of comparing them and deciding whether we need to improve them.

“We don’t get that out of a criminal prosecution.”

Should criminal prosecutions start up after August, with the commission’s hearings only ending in November, Little expects a lack of participation from many parties out of their fears of possible self-incrimination.

“It would mean that the Royal Commission would then have to basically be delayed until all the criminal prosecutions are dealt with.”

Little suspects that these delays could hold up the commission for two to three years.

“Memories will be dimmed, it will be harder to get an accurate picture about what exactly happened.

“But it would be another several years the underground mining industry in New Zealand will be working under regulations which, on the face of it and from experience, appear to be unsafe.”

While it’s not yet clear whether prosecutions will interfere with the Royal Commission, Little does recognise the need for them.

“If people have acted negligently, and acted so negligently that it’s criminal, they ought to be held to account for it.”

The union leader also notes that the New Zealand Police have a proven track record of taking on risky cases, and have even prosecuted surgeons for unsafe surgery practices.

“They don’t hold back when they think there is a case to answer.”

The first in a series of explosions struck the Pike River mine on November 19, claiming 29 lives.

Hopes of finding more survivors from the mine ended after the second underground explosion on November 24.

Damage from subsequent methane explosions and a fire underground further complicated the recovery efforts.