Police have admitted they didn't look at what is effectively the black box of the Pike River Mine disaster beyond the first explosion.
Some Pike families say this was negligent because the second explosion changed everything - ending the rescue operation and all hope of finding any of the 29 men alive.
But they also say the data on the so-called black box could offer some closure.
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We know the first explosion at the Pike River Mine in 2010 was survivable because Daniel Rockhouse and Russell Smith made it out, and there were hopes other survivors were still trapped inside.
"I have to keep believing that there's every chance they're alive," mine boss Peter Whittall said at the time.
But on November 24, five days after that explosion, time ran out for any possible survivors and their families with the devastating second explosion.
Since then, Pike families have been keen to know what happened between the two explosions. It turns out there is a way to find out - it's called SCADA data.
"The best analogy you could make of SCADA is it is exactly the same as a black box in an aircraft," electrical expert Richard Healey says.
SCADA monitors all the cameras, the communications, the pumping stations, the gas and fluid levels and the electrics. It holds all the clues to what causes mine explosions.
But police have admitted to Newshub that they've only looked at it up to the first explosion.
The head of the Pike investigation, Detective Superintendent Peter Read, says the police were concentrating on that first blast so the data after that was of no relevance to them.
"So we haven't looked at it, and we didn't save it."
Dean Dunbar, whose 17-year-old son Joseph died in the mine, has been trying to get the data after the first explosion from the police - to no avail.
"Emails day after day after day, deny deny deny, it's a classic defence," he says.
Initially, Read denied having any SCADA beyond the first blast, but after the Pike River Recovery Agency said police had SCADA up to the second explosion and considerably more, Read confirmed they actually have data from before the first blast until after the second.
He said the server it was saved onto was obsolete, so they had problems accessing it.
"We've had to go out as a family and do our own investigation work," former Pike families' spokesperson Bernie Monk says.
"We've had to put the pressure on them to come back to us and admit that there's all this stuff there that we've been asking for."
Read has now found a forensic analyst who will begin accessing the data this week, which is good because experts have told Newshub that in mine disasters around the world the first thing investigators do is obtain all the Scada.
"Protecting SCADA would have been one of the first things the police should have done," Healey says.
"At the top of their priorities, because SCADA is a robust source of evidence and a reliable source of evidence."
One theory is that turning on a conveyer belt sparked the second blast. SCADA data could prove that one way or the other.
"Bernie and I and other family members want to know what happened and what went so terribly wrong, and we have every right to know," Dunbar says.
They believe the so-called black box data could hold the answers, and are calling for an independent inquiry into the disaster.
Now police realise they have it, the fathers hope they're a step closer to the truth.