Borehole drilling has resumed at Pike River.
Police announced in September they would drill a further 10 boreholes, taking another five months.
They said the work was imperative to ensure the investigation team could reach a definitive conclusion as to what led to the first explosion that killed 29 men underground on November 19, 2010.
Anna Osborne, a spokeswoman for some of the Pike River families, said police had taken over the site and the Department of Conservation, as landowner, had given permission for the continued drilling.
Work had begun on the boreholes, and the good weather was helping as they worked on the "ragged and rough" tops above the now abandoned coalmine.
"I expect it to take months."
The police would then consult specialists, and hopefully lead to prosecutions, she said.
"They need to make sure they have everything possible they can think of the defence might ask," she said.
"Nothing is promised but I feel quite positive.
"They are spending quite a bit of money. It will hopefully come to a good outcome."
In September, Detective Superintendent Peter Read revealed the first 10 boreholes had not looked at the underground fan, long considered a possible ignition source for the first explosion.
However, they would look at the fan this time.
In 2013, police said there was insufficient evidence to lay criminal charges.
WorkSafe New Zealand dropped 12 health and safety charges against Pike River Coal chief executive Peter Whittall in return for a $3 million payout that was shared among the families. That decision was subsequently found to be unlawful.
